FTIRbaselines.R

# FTIRbaselines: Processes FTIR spectra of natural organic matter by finding exact peak locations, baseline-correcting the peaks, and converting them to relative abundances.
#
# New in this version (Jan. 27, 2017): Also calculates areas for each peak, and exports as CSVs called Raw.Areas, Corr.Areas, Norm.Raw.Areas, and Norm.Corr.Areas (defined similarly to the peak height files). Filenames of peak height output files have also been changed to avoid confusing them with the area files. For peaks that share the same baseline, the baseline remains unchanged and the areas are defined between each endpoint and the trough between the peaks. So to get the total area of the aliphatic region (for example), add the areas of the aliph28 and aliph29 peaks.
#
# Copyright © 2017 Suzanne Hodgkins and Florida State University.
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation, either version 3 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License
# along with this program.  If not, see <http://www.gnu.org/licenses/>.
#
# For details on the use of this program, including a tutorial and
# description of all output files, see the included file
# "procedure for R program.docx".
#
# Contact: Dr. Suzanne Hodgkins, suzanne.b.hodgkins@gmail.com

# Startup notice ----
cat("FTIRbaselines: Copyright © 2017 Suzanne Hodgkins and Florida State University.
This program comes with ABSOLUTELY NO WARRANTY. This is free software, and you
are welcome to redistribute it under the terms of the GNU General Public
License (version 3 or later). This license is included with this program and
is also available at <http://www.gnu.org/licenses/>.")

# Import data ----

filename <- readline("Enter name of csv with FTIR absorbance data: ")
data <- read.csv(filename, header=TRUE, row.names=1)

# Check input data ----

if((as.numeric(row.names(data)[1]) - as.numeric(row.names(data)[2])) != 1) {
 stop("Input CSV must have wavenumbers in the first column in descending order.")
}

# check for absorbance mode
if(max(data) > 5 | is.na(max(data))) {
  stop("Input data must be in Absorbance mode, with no extra rows except for the header row.")
}

# Prepare to analyze data ----

n <- 29  # number of points to differentiate over; must be odd
m <- (n-1)/2

peaks <- c("carb", "arom15", "arom16", "trough16", "acids", "aliph28", "trough28", "aliph29")

# preallocate dataframes
Wp <- data.frame(matrix(nrow=length(data),ncol=length(peaks),dimnames=list(names(data),peaks)))
W1 <- Wp
W2 <- Wp
Ap <- Wp
A1 <- Wp
A2 <- Wp
Ab <- Wp
Acorr <- Wp
success.W1 <- Wp
success.W2 <- Wp
area.wholepeak <- Wp
area.corrpeak <- Wp
notes <- data.frame(aliph.type=rep(NA,length(data)), acids.type=rep(NA,length(data)), notes=rep(NA,length(data)), row.names=names(data))

# Function for finding peak boundaries
minima <- function(region, default=NULL) {
  # region = segment of xydata containing the peak boundary (see definition of xydata in next section)
  # default = wavenumber to use if a suitable minimum is not found

  success <- TRUE # changes to FALSE if the minimum resorts to default

  # First try to find a true local minimum, based on were dy crosses the x-axis and d2y > 0:
  offset.dy <- c(0, region$dy)[1:(length(region$dy))]
  just.crossed <- which(sign(region$dy*offset.dy) == -1 & region$d2y > 0)
  crossing <- c(just.crossed, just.crossed-1)
  if(length(crossing) > 0) {
    # Find the absolute minimum among the local minima candidates.
    index.min <- which(region$y==min(region$y[crossing]) & region$x %in% region$x[crossing])
    # Location of absolute minimum in region of index.min, for cases where multi-point derivative causes slight error.
    # Deactivate if this causes problems.
    index.min <- which(region$y==min(region$y[(index.min-min(m, index.min-1)):(index.min+min(m, nrow(region)-index.min))]) & region$x %in% region$x[(index.min-min(m, index.min-1)):(index.min+min(m, nrow(region)-index.min))])
    # wavenumber of local minimum
    minimum <- region$x[index.min]
  } else {
    # If the above doesn't work, use the maximum of the 2nd derivative if it is positive (i.e. "shoulder minimum"):
    if(max(region$d2y) > 0) {
      minimum <- region$x[which(region$d2y==max(region$d2y))]
    } else {
      # if there are no minima or "shoulder minima", use default
      minimum <- default
      success <- FALSE
    }
  }
  if(length(minimum)>1) {
    cat(paste(" Warning: multiple minima for", default, "peak boundary:", paste(minimum, collapse=" "), "\n"))
  }
  return(list(minimum=minimum, success=success))
}

# Function for finding peaks, for use with acids peak
maxima <- function(region, default=NULL) {
  # region = segment of xydata containing the peak boundary (see definition of xydata in next section)
  # default = wavenumber to use if a suitable minimum is not found

  success <- TRUE # changes to FALSE if the minimum resorts to default

  # First try to find a true local maximum, based on were dy crosses the x-axis and d2y < 0:
  offset.dy <- c(0, region$dy)[1:(length(region$dy))]
  just.crossed <- which(sign(region$dy*offset.dy) == -1 & region$d2y < 0)
  crossing <- c(just.crossed, just.crossed-1)
  if(length(crossing) > 0) {
    # Find the absolute maximum among the local maxima candidates.
    index.max <- which(region$y==max(region$y[crossing]) & region$x %in% region$x[crossing])
    # Location of absolute maximum in region of index.max, for cases where multi-point derivative causes slight error.
    # Deactivate if this causes problems.
    index.max <- which(region$y==max(region$y[(index.max-min(m, index.max-1)):(index.max+min(m, nrow(region)-index.max))]) & region$x %in% region$x[(index.max-min(m, index.max-1)):(index.max+min(m, nrow(region)-index.max))])
    # wavenumber of local maximum
    maximum <- region$x[index.max]
  } else {
    # If the above doesn't work, use the minimum of the 2nd derivative if it is negative (i.e. "shoulder maximum"):
    if(min(region$d2y) < 0) {
      maximum <- region$x[which(region$d2y==min(region$d2y))]
    } else {
      # if there are no maxima or "shoulder maxima", use default
      maximum <- default
      success <- FALSE
    }
  }
  if(length(maximum)>1) {
    cat(paste(" Warning: multiple maxima for", default, "peak:", paste(maximum, collapse=" "), "\n"))
  }
  return(list(maximum=maximum, success=success))
}


# Find peaks and peak boundaries for each spectrum ----

x <- as.numeric(row.names(data))

for(i in seq_along(data)) {
  cat(paste0("Processing ", names(data)[i], " (", i, " of ", length(data), ")\n"))

  y <- data[,i]
  xydata <- data.frame(x=x, y=y)

  # calculate first derivative
  dy <- rep(NA, length(y))
  for(j in (m+1):(length(dy)-m)) {
    dy[j] <- coefficients(lsfit(x[(j-m):(j+m)], y[(j-m):(j+m)]))[2]
  }
  xydata <- cbind(xydata, dy)

  # calculate second derivative
  d2y <- rep(NA, length(y))
  for(j in (2*m+1):(length(d2y)-2*m)) {
    d2y[j] <- coefficients(lsfit(x[(j-m):(j+m)], dy[(j-m):(j+m)]))[2]
  }
  xydata <- cbind(xydata, d2y)

  # Find w1, w2, and location of each peak (can alter ranges as needed).

  # 1030 peak ("carb") ----

  w1.result <- minima(xydata[x %in% 890:920,], default=905)
  w1 <- max(w1.result[[1]]) # the max accounts for the unlikely event where 2 minima were found with exactly the same y
  a1 <- y[x == w1]
  W1[i,"carb"] <- w1
  A1[i,"carb"] <- a1
  success.W1[i,"carb"] <- w1.result[[2]]

  #w2.result <- minima(xydata[x %in% 1100:1150,], default=1135) # lower w2 option
  w2.result <- minima(xydata[x %in% 1150:1210,], default=1185) # higher w2 option
  w2 <- min(w2.result[[1]]) # the min accounts for the unlikely event where 2 minima were found with exactly the same y
  a2 <- y[x == w2]
  W2[i,"carb"] <- w2
  A2[i,"carb"] <- a2
  success.W2[i,"carb"] <- w2.result[[2]]

  # baseline correction calculated for all wavenumbers in peak
  w.wholepeak <- w2:w1
  a.wholepeak <- y[x %in% w.wholepeak]
  a.corrpeak <- a.wholepeak-((a2-a1)*(w.wholepeak-w1)/(w2-w1)+a1)

  # peak areas
  area.wholepeak[i,"carb"] <- sum(a.wholepeak)
  area.corrpeak[i,"carb"] <- sum(a.corrpeak)

  # pick out peak location
  Acorr[i,"carb"] <- max(a.corrpeak)
  Wp[i,"carb"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"carb"]]) # the min accounts for unlikely event of 2 peaks with exactly the same y; the same is true for all other peaks defined as min(w.wholepeak...) etc.
  Ap[i,"carb"] <- a.wholepeak[w.wholepeak==Wp[i,"carb"]]
  Ab[i,"carb"] <- Ap[i,"carb"] - Acorr[i,"carb"]

  rm(w1.result, w2.result, w1, w2, a1, a2, w.wholepeak, a.wholepeak, a.corrpeak)


  # 1510 peak ("arom15") *** NOTE THIS PEAK IS HIGHLY VARIABLE *** ----

  w1.result <- minima(xydata[x %in% 1470:1500,], default=1485)
  w1 <- max(w1.result[[1]])
  a1 <- y[x == w1]
  W1[i,"arom15"] <- w1
  A1[i,"arom15"] <- a1
  success.W1[i,"arom15"] <- w1.result[[2]]

  w2.result <- minima(xydata[x %in% 1515:1540,], default=1535)
  w2 <- min(w2.result[[1]])
  a2 <- y[x == w2]
  W2[i,"arom15"] <- w2
  A2[i,"arom15"] <- a2
  success.W2[i,"arom15"] <- w2.result[[2]]

  #  # redefine either w1 or w2 so that the baseline doesn't cut through part of the graph
  #  if((a2-a1)/(w2-w1) > 0) {
  #    # if baseline slope is positive, slightly increase w1
  #    w1 <- max(x[x %in% w1:(w1+20) & y <= (a1 + 0.005*max(y[x > 1800]))])
  #    w1.result <- list(minimum=w1, success=success.W1[i,"arom15"])
  #    a1 <- y[x == w1]
  #    W1[i,"arom15"] <- w1
  #    A1[i,"arom15"] <- a1
  #    success.W1[i,"arom15"] <- w1.result[[2]]
  #  } else {
  #    # if baseline slope is negative, slightly decrease w2
  #    w2 <- min(x[x %in% (w2-20):w2 & y <= (a2 + 0.005*max(y[x > 1800]))])
  #    w2.result <- list(minimum=w2, success=success.W2[i,"arom15"])
  #    a2 <- y[x == w2]
  #    W2[i,"arom15"] <- w2
  #    A2[i,"arom15"] <- a2
  #    success.W2[i,"arom15"] <- w2.result[[2]]
  #  }

  # baseline correction calculated for all wavenumbers in peak
  w.wholepeak <- w2:w1
  a.wholepeak <- y[x %in% w.wholepeak]
  a.corrpeak <- a.wholepeak-((a2-a1)*(w.wholepeak-w1)/(w2-w1)+a1)

  # peak areas
  area.wholepeak[i,"arom15"] <- sum(a.wholepeak)
  area.corrpeak[i,"arom15"] <- sum(a.corrpeak)

  # pick out peak location
  Acorr[i,"arom15"] <- max(a.corrpeak)
  if(Acorr[i,"arom15"]==0) {
    #what to do if there is no arom15 peak, i.e. a.corrpeak is negative except at endpoints
    Wp[i,"arom15"] <- 1510 # use this as a default value for Wp
    Acorr[i,"arom15"] <- a.corrpeak[w.wholepeak==Wp[i,"arom15"]] # redefine Acorr at Wp
    Ap[i,"arom15"] <- a.wholepeak[w.wholepeak==Wp[i,"arom15"]]
    Ab[i,"arom15"] <- Ap[i,"arom15"] - Acorr[i,"arom15"]
  } else {   # normal arom15 peak
    Wp[i,"arom15"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"arom15"]])
    Ap[i,"arom15"] <- a.wholepeak[w.wholepeak==Wp[i,"arom15"]]
    Ab[i,"arom15"] <- Ap[i,"arom15"] - Acorr[i,"arom15"]
  }

  rm(w1.result, w2.result, w1, w2, a1, a2, w.wholepeak, a.wholepeak, a.corrpeak)


  # 1630 and 1720 peaks ("arom16" and "acids") ----

  # Processes of defining w1 and w2 are a bit different, but still use the same variable names:
  if (A2[i,"arom15"] != min(y[x %in% W2[i,"arom15"]:1590])) {
    # case where there is another local minimum in y after w2 of the arom15 peak
    w1.result <- list(minimum=x[y==min(y[x %in% W2[i,"arom15"]:1590])], success=TRUE)
  } else {
    # w1 for these peaks is the w2 of the arom15 peak
    w1.result <- list(minimum=W2[i,"arom15"], success=success.W2[i,"arom15"])
  }
  w1 <- max(w1.result[[1]])
  a1 <- y[x == w1]
  W1[i,"arom16"] <- w1
  A1[i,"arom16"] <- a1
  success.W1[i,"arom16"] <- w1.result[[2]]
  W1[i,"trough16"] <- w1
  A1[i,"trough16"] <- a1
  success.W1[i,"trough16"] <- w1.result[[2]]
  W1[i,"acids"] <- w1
  A1[i,"acids"] <- a1
  success.W1[i,"acids"] <- w1.result[[2]]

  # w2 for these peaks based on first wavenumber that is "close" to the absolute minimum
  w2 <- min(x[x %in% 1760:1850 & y <= (min(y[x %in% 1760:1850]) + 0.01*max(y[x > 1800]))])
  w2.result <- list(minimum=w2, success=TRUE)
  a2 <- y[x == w2]
  W2[i,"arom16"] <- w2
  A2[i,"arom16"] <- a2
  success.W2[i,"arom16"] <- w2.result[[2]]
  W2[i,"trough16"] <- w2
  A2[i,"trough16"] <- a2
  success.W2[i,"trough16"] <- w2.result[[2]]
  W2[i,"acids"] <- w2
  A2[i,"acids"] <- a2
  success.W2[i,"acids"] <- w2.result[[2]]

  # baseline correction calculated for all wavenumbers in peak
  w.wholepeak <- w2:w1
  a.wholepeak <- y[x %in% w.wholepeak]
  a.corrpeak <- a.wholepeak-((a2-a1)*(w.wholepeak-w1)/(w2-w1)+a1)

  # Now comes the hard part:
  # Separately find both peaks and the trough.
  # The arom16 peak is probably easiest, so find this first.

  # pick out 1630 peak location (only check wavenumbers up to a set point)
  Acorr[i,"arom16"] <- max(a.corrpeak[w.wholepeak < 1660])
  if(Acorr[i,"arom16"] == 0) {
    # what to do if there is no arom16 peak, i.e. a.corrpeak is negative except at endpoint
    Wp[i,"arom16"] <- 1630 # use this as a default value for Wp
    Acorr[i,"arom16"] <- a.corrpeak[w.wholepeak==Wp[i,"arom16"]] # redefine Acorr at Wp
    Ap[i,"arom16"] <- a.wholepeak[w.wholepeak==Wp[i,"arom16"]]
    Ab[i,"arom16"] <- Ap[i,"arom16"] - Acorr[i,"arom16"]
  } else {   # normal arom16 peak
    Wp[i,"arom16"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"arom16"]])
    Ap[i,"arom16"] <- a.wholepeak[w.wholepeak==Wp[i,"arom16"]]
    Ab[i,"arom16"] <- Ap[i,"arom16"] - Acorr[i,"arom16"]
  }

  # find an initial guess for the trough using the minima function
  # use a range of arom16+20 --> min(1740, (w2-20)) (min with 1740 is new, MAY CHANGE THIS LATER)

  default.trough16 <- 1685
  default.acids <- 1725

  tr.ini <- minima(xydata[x %in% max(1650, Wp[i,"arom16"]+20):min(1740, (w2-20)),], default=default.trough16)[[1]]

  # pick out acids peak location
  if(all(dy[x %in% max(1650, Wp[i,"arom16"]+20):min(1740, (w2-20))] < 0)) {
    # weak or absent acids peak, i.e. dy is always negative
    acids.result <- maxima(xydata[x %in% max(tr.ini, 1685):w2,], default=default.acids)
    Wp[i,"acids"] <- min(acids.result[[1]])
    Acorr[i,"acids"] <- a.corrpeak[w.wholepeak==Wp[i,"acids"]]
    Ap[i,"acids"] <- a.wholepeak[w.wholepeak==Wp[i,"acids"]]
    Ab[i,"acids"] <- Ap[i,"acids"] - Acorr[i,"acids"]
    notes[i, "acids.type"] <- ifelse(acids.result[[2]], "shoulder", "no peak")
    rm(acids.result)
  } else {
    # case where there is a local maximum in region of acids peak, i.e. dy > 0 in part of this region
    if(max(a.corrpeak[w.wholepeak > max(tr.ini, 1685)]) != 0) {
      # case where there is a true/normal acids peak above the baseline
      Acorr[i,"acids"] <- max(a.corrpeak[w.wholepeak > max(tr.ini, 1685)])
      Wp[i,"acids"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"acids"]])
      Ap[i,"acids"] <- a.wholepeak[w.wholepeak==Wp[i,"acids"]]
    } else {
      # case where there is a true acids peak, but it is below baseline
      # in this case, non-baseline-corrected absorbances are used to find the peak
      Ap[i,"acids"] <- max(a.wholepeak[w.wholepeak > max(tr.ini, 1685)])
      Wp[i,"acids"] <- min(w.wholepeak[a.wholepeak==Ap[i,"acids"]])
      Acorr[i,"acids"] <- a.corrpeak[w.wholepeak==Wp[i,"acids"]]
    }
    Ab[i,"acids"] <- Ap[i,"acids"] - Acorr[i,"acids"]
    notes[i, "acids.type"] <- "peak"
  }

  # pick out "true" trough location, defined based on whether acids is a real peak
  if(notes[i, "acids.type"] == "peak") {
    Acorr[i,"trough16"] <- min(a.corrpeak[w.wholepeak %in% Wp[i,"arom16"]:Wp[i,"acids"]])
    Wp[i,"trough16"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"trough16"]])
  } else if (notes[i, "acids.type"] == "shoulder") {
    Wp[i,"trough16"] <- min(tr.ini)
    Acorr[i,"trough16"] <- a.corrpeak[w.wholepeak==Wp[i,"trough16"]]
  } else { # acids.type is "no peak"
    Wp[i,"trough16"] <- default.trough16
    Acorr[i,"trough16"] <- a.corrpeak[w.wholepeak==Wp[i,"trough16"]]
  }
  Ap[i,"trough16"] <- a.wholepeak[w.wholepeak==Wp[i,"trough16"]]
  Ab[i,"trough16"] <- Ap[i,"trough16"] - Acorr[i,"trough16"]

  # append "negative" to acids.type if Acorr is negative for either acids or trough16
  if(Acorr[i,"trough16"] < 0 | Acorr[i,"acids"] < 0) {
    notes[i, "acids.type"] <- paste0(notes[i, "acids.type"], ", negative")
  }

  # peak area of arom16 (<= trough16)
  area.wholepeak[i,"arom16"] <- sum(a.wholepeak[w.wholepeak %in% w1:Wp[i,"trough16"]])
  area.corrpeak[i,"arom16"] <- sum(a.corrpeak[w.wholepeak %in% w1:Wp[i,"trough16"]])
  # peak area of acids (> trough16)
  area.wholepeak[i,"acids"] <- sum(a.wholepeak[w.wholepeak %in% (Wp[i,"trough16"]+1):w2])
  area.corrpeak[i,"acids"] <- sum(a.corrpeak[w.wholepeak %in% (Wp[i,"trough16"]+1):w2])

  rm(w1.result, w2.result, w1, w2, a1, a2, w.wholepeak, a.wholepeak, a.corrpeak, tr.ini, default.trough16, default.acids)


  # 2850 and 2920 peaks ("aliph28" and "aliph29") ----

  # w1 for these peaks is a constant, which can be changed globally if needbe
  w1.result <- list(minimum=2750, success=TRUE)
  w1 <- max(w1.result[[1]])
  a1 <- y[x == w1]
  W1[i,"aliph28"] <- w1
  A1[i,"aliph28"] <- a1
  success.W1[i,"aliph28"] <- w1.result[[2]]
  W1[i,"trough28"] <- w1
  A1[i,"trough28"] <- a1
  success.W1[i,"trough28"] <- w1.result[[2]]
  W1[i,"aliph29"] <- w1
  A1[i,"aliph29"] <- a1
  success.W1[i,"aliph29"] <- w1.result[[2]]

  #w2 for these peaks is based on local minimum
  w2.result <- minima(xydata[x %in% 2950:3050,], default=3000)
  w2 <- min(w2.result[[1]])
  a2 <- y[x == w2]
  W2[i,"aliph28"] <- w2
  A2[i,"aliph28"] <- a2
  success.W2[i,"aliph28"] <- w2.result[[2]]
  W2[i,"trough28"] <- w2
  A2[i,"trough28"] <- a2
  success.W2[i,"trough28"] <- w2.result[[2]]
  W2[i,"aliph29"] <- w2
  A2[i,"aliph29"] <- a2
  success.W2[i,"aliph29"] <- w2.result[[2]]

  # baseline correction calculated for all wavenumbers in peak
  w.wholepeak <- w2:w1
  a.wholepeak <- y[x %in% w.wholepeak]
  a.corrpeak <- a.wholepeak-((a2-a1)*(w.wholepeak-w1)/(w2-w1)+a1)

  # pick out peak locations

  # The aliphatic region can be one of 3 basic shapes.
  # To test them, perform 2 checks:
  # (1) check if maximum is close to 2920
  # (2) if max is close to 2920, check if there is any local minimum in a.wholepeak or (if not) a.corrpeak between 2850 and 2920

  if(max(w.wholepeak[a.wholepeak==max(a.wholepeak)]) %in% 2915:w2) {
    # case where maximum is close to 2920 (or higher)
    if(!any(w.wholepeak[a.wholepeak==min(a.wholepeak[w.wholepeak %in% 2854:2913])] %in% c(2854,2913))) {
      # case where there is a local minimum in a.wholepeak between 2854 and 2913
      # (i.e., the absolute minimum of this range is not one of the endpoints)
      type <- "two separated peaks"
    } else if(sum(y[x %in% 2920:2850]-((y[x==2920]-y[x==2850])*((2920:2850)-2850)/(2920-2850)+y[x==2850])) < 0) {
      # case where there is no local minimum in a.wholepeak,
      # but absorbances between 2850 and 2920 are below a diagonal between these points
      type <- "two unseparated peaks"
    } else {
      # case where none of mid-region is concave up, indicating singlet with max at 2920
      type <- "one peak"
    }
  } else {
    # case where maximum is not close to 2920
    type <- "one peak"
  }
  notes[i,"aliph.type"] <- type

  if(type == "one peak") {
    # set aliph29 as peak maximum, regardless of where this maximum is
    # then set trough28 and aliph28 the same as aliph29
    Acorr[i,"aliph29"] <- max(a.corrpeak)
    Wp[i,"aliph29"] <- max(w.wholepeak[a.corrpeak==Acorr[i,"aliph29"]])
    Ap[i,"aliph29"] <- a.wholepeak[w.wholepeak==Wp[i,"aliph29"]]
    Ab[i,"aliph29"] <- Ap[i,"aliph29"] - Acorr[i,"aliph29"]

    Acorr[i,"trough28"] <- Acorr[i,"aliph29"]
    Wp[i,"trough28"] <- Wp[i,"aliph29"]
    Ap[i,"trough28"] <- Ap[i,"aliph29"]
    Ab[i,"trough28"] <- Ab[i,"aliph29"]

    Acorr[i,"aliph28"] <- Acorr[i,"aliph29"]
    Wp[i,"aliph28"] <- Wp[i,"aliph29"]
    Ap[i,"aliph28"] <- Ap[i,"aliph29"]
    Ab[i,"aliph28"] <- Ab[i,"aliph29"]

  } else if(type == "two separated peaks") {
    Acorr[i,"aliph29"] <- max(a.corrpeak[w.wholepeak %in% 2900:w2])
    Wp[i,"aliph29"] <- max(w.wholepeak[a.corrpeak==Acorr[i,"aliph29"]])
    Ap[i,"aliph29"] <- a.wholepeak[w.wholepeak==Wp[i,"aliph29"]]
    Ab[i,"aliph29"] <- Ap[i,"aliph29"] - Acorr[i,"aliph29"]

    Acorr[i,"trough28"] <- min(a.corrpeak[w.wholepeak %in% 2854:Wp[i,"aliph29"]])
    Wp[i,"trough28"] <- max(w.wholepeak[a.corrpeak==Acorr[i,"trough28"]])
    Ap[i,"trough28"] <- a.wholepeak[w.wholepeak== Wp[i,"trough28"]]
    Ab[i,"trough28"] <- Ap[i,"trough28"] - Acorr[i,"trough28"]

    Acorr[i, "aliph28"] <- max(a.corrpeak[w.wholepeak %in% w1:Wp[i,"trough28"]])
    Wp[i,"aliph28"] <- min(w.wholepeak[a.corrpeak==Acorr[i,"aliph28"]])
    Ap[i,"aliph28"] <- a.wholepeak[w.wholepeak==Wp[i,"aliph28"]]
    Ab[i,"aliph28"] <- Ap[i,"aliph28"] - Acorr[i,"aliph28"]

  } else { # type == "two unseparated peaks"
    Acorr[i,"aliph29"] <- max(a.corrpeak[w.wholepeak %in% 2900:w2])
    Wp[i,"aliph29"] <- max(w.wholepeak[a.corrpeak==Acorr[i,"aliph29"]])
    Ap[i,"aliph29"] <- a.wholepeak[w.wholepeak==Wp[i,"aliph29"]]
    Ab[i,"aliph29"] <- Ap[i,"aliph29"] - Acorr[i,"aliph29"]

    Acorr[i,"trough28"] <- min(a.corrpeak[w.wholepeak %in% 2854:Wp[i,"aliph29"]])
    Wp[i,"trough28"] <- max(w.wholepeak[a.corrpeak==Acorr[i,"trough28"]])
    Ap[i,"trough28"] <- a.wholepeak[w.wholepeak== Wp[i,"trough28"]]
    Ab[i,"trough28"] <- Ap[i,"trough28"] - Acorr[i,"trough28"]

    # manually specify aliph28
    # since two unseparated peaks otherwise produces unpredictable results
    Wp[i,"aliph28"] <- 2850
    Acorr[i,"aliph28"] <- a.corrpeak[w.wholepeak==Wp[i,"aliph28"]]
    Ap[i,"aliph28"] <- a.wholepeak[w.wholepeak==Wp[i,"aliph28"]]
    Ab[i,"aliph28"] <- Ap[i,"aliph28"] - Acorr[i,"aliph28"]
  }

  # peak area of aliph28 (<= trough28)
  area.wholepeak[i,"aliph28"] <- sum(a.wholepeak[w.wholepeak %in% w1:Wp[i,"trough28"]])
  area.corrpeak[i,"aliph28"] <- sum(a.corrpeak[w.wholepeak %in% w1:Wp[i,"trough28"]])
  # peak area of aliph29 (> trough28)
  area.wholepeak[i,"aliph29"] <- sum(a.wholepeak[w.wholepeak %in% (Wp[i,"trough28"]+1):w2])
  area.corrpeak[i,"aliph29"] <- sum(a.corrpeak[w.wholepeak %in% (Wp[i,"trough28"]+1):w2])

  rm(w1.result, w2.result, w1, w2, a1, a2, w.wholepeak, a.wholepeak, a.corrpeak, type)


  rm(xydata, y, dy, d2y)


}

# Show plots for each peak in each sample ----
cat(paste("Spectra with baselines and peak locations will be shown for all", length(data), "samples."))
plots.prompt <- readline("Prompt for notes on each spectrum, which will be stored in output? (y/n) ")
while(!any(plots.prompt == c('y','Y','n','N'))) {
  plots.prompt <- readline(paste("Invalid response. Prompt for notes on each spectrum? Type Y or N. "))
}

col.peaks <- rep(NA, length(peaks))
names(col.peaks) <- peaks
col.peaks['carb'] <- 'blue'
col.peaks['arom15'] <- 'red'
col.peaks['arom16'] <- 'purple3'
col.peaks['trough16'] <- 'deepskyblue3'
col.peaks['acids'] <- 'forestgreen'
col.peaks['aliph28'] <- 'darkorange3'
col.peaks['trough28'] <- 'gold4'
col.peaks['aliph29'] <- 'orangered3'

lty.peaks <- ifelse(peaks=="trough16" | peaks=="trough28", "dashed", "solid")
names(lty.peaks) <- peaks

for(i in seq_along(data)) {
  plot(x, data[,i], type="l", xaxp=c(700,4000,33), xaxs='i', yaxs='i', main=names(data)[i], xlab="wavenumber", ylab="Absorbance")

  for(j in seq_along(peaks)) {
    segments(W1[i,j], A1[i,j], W2[i,j], A2[i,j], col="green")                        # baseline
    segments(Wp[i,j], Ap[i,j], Wp[i,j], Ab[i,j], col=col.peaks[j], lty=lty.peaks[j]) # Acorr
    segments(W1[i,j], A1[i,j], W1[i,j], 0, lty="dotted", col="gray50") # connect endpoints to x-axis
    segments(W2[i,j], A2[i,j], W2[i,j], 0, lty="dotted", col="gray50") # connect endpoints to x-axis
    #     points(c(W1[i,j], W2[i,j]), c(A1[i,j], A2[i,j]), col="gray50")
    #     points(c(Wp[i,j], Wp[i,j]), c(Ap[i,j], Ab[i,j]), col="gray50")
  }
  if(plots.prompt == 'y' | plots.prompt == 'Y') {
    notes[i,"notes"] <- readline("Do these peak baseline corrections look OK? Type any notes, or just press ENTER. ")
  }
}

# Show plots again zoomed in on the aromatic/carboxyl region, if the user says to.

show16 <- readline("Show spectra again, zoomed in on the region from 1450-1850 cm^-1? (y/n) ")
while(!any(show16 == c('y','Y','n','N'))) {
  show16 <- readline("Invalid response. Show spectra again, zoomed in to 1450-1850 cm^-1? Type Y or N. ")
}

if(show16 == 'y' | show16 == 'Y') {
  for(i in seq_along(data)) {

    plot(x, data[,i], type="l", xlim=c(1470,1850), ylim=c(0, max(data[x %in% 1470:1850,i])), main=names(data)[i], xlab="wavenumber", ylab="Absorbance")

    segments(W1[i,"arom15"], A1[i,"arom15"], W2[i,"arom15"], A2[i,"arom15"], col="green")      # baseline
    segments(Wp[i,"arom15"], Ap[i,"arom15"], Wp[i,"arom15"], Ab[i,"arom15"], col=col.peaks["arom15"]) # Acorr
    segments(W1[i,"arom15"], A1[i,"arom15"], W1[i,"arom15"], 0, lty="dotted", col="gray50") # connect endpoints to x-axis
    segments(W2[i,"arom15"], A2[i,"arom15"], W2[i,"arom15"], 0, lty="dotted", col="gray50") # connect endpoints to x-axis
    points(c(W1[i,"arom15"], W2[i,"arom15"]), c(A1[i,"arom15"], A2[i,"arom15"]), col="gray50")
    points(c(Wp[i,"arom15"], Wp[i,"arom15"]), c(Ap[i,"arom15"], Ab[i,"arom15"]), col="gray50")

    segments(W1[i,'arom16'], A1[i,'arom16'], W2[i,'arom16'], A2[i,'arom16'], col="green") # baseline
    segments(Wp[i,'arom16'], Ap[i,'arom16'], Wp[i,'arom16'], Ab[i,'arom16'], col=col.peaks['arom16'], lty=lty.peaks['arom16'])
    segments(Wp[i,'trough16'], Ap[i,'trough16'], Wp[i,'trough16'], Ab[i,'trough16'], col=col.peaks['trough16'], lty=lty.peaks['trough16'])
    segments(Wp[i,'acids'], Ap[i,'acids'], Wp[i,'acids'], Ab[i,'acids'], col=col.peaks['acids'], lty=lty.peaks['acids'])
    points(c(W1[i,'arom16'], W2[i,'arom16']), c(A1[i,'arom16'], A2[i,'arom16']), col="gray50")
    points(c(Wp[i,'arom16'], Wp[i,'arom16']), c(Ap[i,'arom16'], Ab[i,'arom16']), col="gray50")
    points(c(Wp[i,'trough16'], Wp[i,'trough16']), c(Ap[i,'trough16'], Ab[i,'trough16']), col="gray50")
    points(c(Wp[i,'acids'], Wp[i,'acids']), c(Ap[i,'acids'], Ab[i,'acids']), col="gray50")
    segments(W1[i,"arom16"], A1[i,"arom16"], W1[i,"arom16"], 0, lty="dotted", col="gray50") # connect endpoints to x-axis
    segments(W2[i,"arom16"], A2[i,"arom16"], W2[i,"arom16"], 0, lty="dotted", col="gray50") # connect endpoints to x-axis

    if(plots.prompt == 'y' | plots.prompt == 'Y') {
      notes.addon <- readline("Do these peak baseline corrections look OK? Type any notes, or just press ENTER. ")
      if(notes.addon != "") {
        if(notes[i,"notes"] == "") {
          notes[i,"notes"] <- paste0("aromatic/carboxyl region: ", notes.addon)
        } else {
          notes[i,"notes"] <- paste0(notes[i,"notes"], ". aromatic/carboxyl region: ", notes.addon)
        }
      }
    }
  }
}


# Calculate areas and mineral indices (780 peak, for silicates; constant and has no baseline) ----
area <- apply(data, 2, sum)
silicate780 <- as.numeric(data[x==780,])
norm.silicate780 <- silicate780/area
area_and_silicate <- data.frame(area, silicate780, norm.silicate780)

# Normalize to area ----
norm.Ap <- Ap/area
norm.Acorr <- Acorr/area
norm.area.wholepeak <- area.wholepeak/area
norm.area.corrpeak <- area.corrpeak/area

# Export data ----

dataset.name <- readline("ENTER NAME OF FOLDER FOR OUTPUTTING DATA (if different from original csv filename): ")

if(dataset.name == "") {
  dataset.name <- gsub(".csv", "", filename, fixed=TRUE) # get name of dataset from original csv filename
}
dataset.name <- gsub("\\W", "_", dataset.name) # replace all non-alphanumeric characters with "_"
dir.create(dataset.name)  # create a new folder for output files

write.csv(data, file.path(getwd(), dataset.name, filename))
write.csv(area_and_silicate, file.path(getwd(), dataset.name, "TotalArea.and.780.csv"))
write.csv(Wp, file.path(getwd(), dataset.name, "Wp.csv"))
write.csv(W1, file.path(getwd(), dataset.name, "W1.csv"))
write.csv(W2, file.path(getwd(), dataset.name, "W2.csv"))
write.csv(Ap, file.path(getwd(), dataset.name, "Heights_Raw.csv"))
write.csv(Acorr, file.path(getwd(), dataset.name, "Heights_Corr.csv"))
write.csv(norm.Ap, file.path(getwd(), dataset.name, "Heights_Norm.Raw.csv"))
write.csv(norm.Acorr, file.path(getwd(), dataset.name, "Heights_Norm.Corr.csv"))
write.csv(area.wholepeak, file.path(getwd(), dataset.name, "Areas_Raw.csv"))
write.csv(area.corrpeak, file.path(getwd(), dataset.name, "Areas_Corr.csv"))
write.csv(norm.area.wholepeak, file.path(getwd(), dataset.name, "Areas_Norm.Raw.csv"))
write.csv(norm.area.corrpeak, file.path(getwd(), dataset.name, "Areas_Norm.Corr.csv"))
write.csv(success.W1, file.path(getwd(), dataset.name, "success.W1.csv"))
write.csv(success.W2, file.path(getwd(), dataset.name, "success.W2.csv"))
write.csv(notes, file.path(getwd(), dataset.name, "Notes.csv"))