User Guide 1.8.0
In order to use DDS in your Spark shell, you need to add it to your classpath and import the DDS core functions. Depending on the Scala version your Spark is compiled in, select the correct jar. Assuming your Spark is built with 2.10, start your Spark shell with the following parameter and import the core functionality:
spark-shell --jars spawncamping-dds-1.8.0_2.10.jarimport de.frosner.dds.core.DDS._DDS comes with a lightweight web server that serves the results and charts to your browser. It pushes JSON objects to the JavaScript front-end that will then display them using HTML, CSS and SVG. The server needs to be started once after the Spark shell has loaded. It can be used for the entire session. However, you can stop and restart it as often as you like.
Note that a visualization is served only once. So currently only one browser window is able to consume the result (the one that asks quickest). However, if you want the current visualization not to be refreshed, there is a small 
icon in the top right corner of the screen. Clicking this icon will prevent the front-end from talking to the back-end. This allows to have multiple visualizations open at once.
You can change the visualization title in the top left corner to save it for later reference or show it to your colleagues.
The server can be started by calling the start() function in the Spark shell. You can also specify the interface and port the server should listen to. To start the server listening to 192.168.0.5:8081, execute the following command:
start("192.168.0.5", 8081)You can also protect your web UI with a password:
start("192.168.0.5", 8081, "pasw1234")Note, that this mechanism uses basic HTTP authentication which transmits the password unencrypted. That means you should not reuse any important passwords here and do not rely on the password staying secure when transmitting it over the internet.
The server can be stopped by calling the stop() function in the Spark shell.
To get a list of all available functions use the help() function. To get help for particular functions, you can pass the function name to help(name: String).
Besides the functions based on RDDs, DDS offers a bunch of generic plotting functions not related to Spark. They can be used to plot charts or display tables in the browser from any data source you have.
line[N](values: Seq[N])(implicit num: Numeric[N])Prints a line chart with the given values and a default label.
lines[N](labels: Seq[String], values: Seq[Seq[N]])(implicit num: Numeric[N])Prints a line chart with multiple lines. The label labels(x) corresponds to the value sequence values(x).
bar[N](values: Seq[N])(implicit num: Numeric[N])Prints a bar chart showing the given counts on an indexed axis and a default label.
bar[N](values: Seq[N], categories: Seq[String])(implicit num: Numeric[N])Prints a bar chart showing the given counts on a categorical axis with a default label. There must be as many categories as there are counts.
bars[N](labels: Seq[String], values: Seq[Seq[N]])(implicit num: Numeric[N])Prints a bar chart with multiple bars on an indexed axis. The label labels(x) corresponds to the value sequence values(x).
bars[N](labels: Seq[String], values: Seq[Seq[N]], categories: Seq[String])
(implicit num: Numeric[N])Prints a bar chart with multiple bars on a categorical axis. The label labels(x) corresponds to the value sequence values(x). There must be a category for each value.
pie[K, V](keyValuePairs: Iterable[(K, V)])(implicit num: Numeric[V])Prints a pie chart with one segment for each key-value pair in the input collection. The keys are assumed to be unique (e.g. values already reduced).
scatter[N1, N2](values: Seq[(N1, N2)])
(implicit num1: Numeric[N1] = null, num2: Numeric[N2] = null)Prints a scatter plot of the given (x, y) sequence. X and Y axes can be either numeric or non-numeric.
heatmap[N](values: Seq[Seq[N]], rowNames: Seq[String] = null,
colNames: Seq[String] = null)(implicit num: Numeric[N])Draws a heat map visualizing the given matrix. values(i)(j) corresponds to the element in the ith row and jth column of the matrix. If no row or column names are specified, they will be numbered.
histogram[N1, N2](bins: Seq[N1], frequencies: Seq[N2])
(implicit num1: Numeric[N1], num2: Numeric[N2])Plots a histogram chart visualizing the given bins and frequencies. The bins are defined by their borders. To specify n bins, you need to pass n+1 borders and n frequencies.
Example:
- 5 people are between 0 and 18 years old, 10 people between 18 and 25
- bins = [0, 18, 25], frequencies = [5, 10]
show[V](sequence: Seq[V])(implicit tag: TypeTag[V])Shows the given value sequence in a table. DDS can show sequences of simple values (e.g. strings, numbers) or composite ones (collections, case classes). The values of that sequence need to have a type tag, i.e. if they are custom classes they need to be defined top level.
table(head: Seq[String], rows: Seq[Seq[Any]])Prints a table with the given row-wise data. The head(x) corresponds to each column, e.g. rows(0)(x).
If the table contains optional values (represented by Scala's Option[T] monad), they will be treated as JavaScript null by the front-end and displayed as empty cells if they are missing.
graph[ID, VL, EL](vertices: Seq[(ID, VL)], edges: Iterable[(ID, ID, EL)])Displays a graph defined by the given vertices and edges. A vertex is represented by a pair of an identifier and a label. Edges are pairs of source and target vertex identifiers. You can specify a vertex label (VL) as well as an edge label (EL) for each vertex and edge, respectively.
show[V](rdd: RDD[V], sampleSize: Int = 100)(implicit tag: TypeTag[V])Prints the first lines of the given RDD in a table. The second (optional) argument determines the number of rows to show. DDS can show RDDs of simple values (e.g. strings, numbers) or composite ones (collections, case classes), as well as SchemaRDDs. The values of that RDD need to have a type tag, i.e. if they are custom classes they need to be defined top level.
If the RDD has a schema associated with the columns, DDS will display the column type and the nullable flag in the column header. A nullable age column would show Age [Double*], while an id column might be ID [String], because it is not nullable.
bar[V](values: RDD[V])Prints a bar chart visualizing the count of all distinct values in this RDD. It is recommended to execute it only on non-numeric value RDDs. Use the histogram function for numeric RDDs instead.
pie[V](values: RDD[V])Prints a pie chart visualizing the count of all distinct values in this RDD. It is recommended to execute it only on non-numeric value RDDs. Use the histogram function for numeric RDDs instead.
histogram[N](values: RDD[N], numBuckets: Int = 100)(implicit num: Numeric[N])Prints a histogram visualizing the given numerical RDD. The second (optional) parameter specifies the number of evenly distributed buckets.
histogram[N1, N2](values: RDD[N1], buckets: Seq[N2])
(implicit num1: Numeric[N1], num2: Numeric[N2])Prints a histogram visualizing the given numerical RDD. The second parameter specifies the buckets to use. Example: To get two buckets, one from 0 to 5 and another one from 5 to 10, you can to pass buckets = List(0,5,10).
groupAndPie[K, N](readyToGroup: RDD[(K, N)])
(reduceFunction: (N, N) => N)
(implicit num: Numeric[N])Computes a pie chart visualizing the numeric values per group. It is assumed that there are key-value pairs in each input row, where the key can be used for grouping. DDS will apply the given reduce function to the values of each group before plotting the reduced value in a segment.
pieGroups[K, N](grouped: RDD[(K, Iterable[N])])
(reduceFunction: (N, N) => N)
(implicit num: Numeric[N])Computes a pie chart visualizing the numeric values per group. It is assumed that there is one input row per group and is usually a result of a group-by operation on an RDD. DDS will apply the given reduce function to the values of each group before plotting the reduced value in a segment.
summarize[N](values: RDD[N])(implicit num: Numeric[N] = null)Shows some basic summary statistics for the given RDD. If the RDD has numeric values, count, sum, min, max, mean, stdev, and variance are calculated. If the RDD has nominal values, DDS will calculate mode and cardinality for you.
groupAndSummarize[K, N](readyToGroup: RDD[(K, N)])(implicit num: Numeric[N])Shows some basic summary statistics for each of the groups defined by the given key. It is assumed that there are key-value pairs in each input row, where the key can be used for grouping.
summarizeGroups[K, N](grouped: RDD[(K, Iterable[N])])
(implicit num: Numeric[N])Shows some basic summary statistics for each of the given groups. It is assumed that there is one input row per group and is usually a result of a group-by operation on an RDD.
correlation(rdd: SchemaRDD)Computes and shows the Pearson correlation matrix of all numerical columns in the given table. If there are missing values, DDS will only use pairwise complete observations for calculating the correlation of two columns / variables.
mutualInformation(rdd: SchemaRDD)Computes and shows a mutual information matrix of all columns in the given table. As of today, numerical values are not binned automatically, so it is strongly advised to bin them before applying this function, as mutual information only works for nominal attributes.
Note that the mutual information values are not normalized so it is not always useful to compare the values directly without taking the entropy of each column into account.
median[N: ClassTag](values: RDD[N])
(implicit num: Numeric[N] = null)Calculates the median of a given numeric data set. Note that this operation can be computationally expensive, as it requires a distributed sort and lookup.
showVertexSample[VD, ED](graph: Graph[VD, ED],
sampleSize: Int = 20,
vertexFilter: (VertexId, VD) => Boolean =
(id: VertexId, attr: VD) => true)Plots a sample of the given GraphX graph based on the vertex set. DDS will sample the graph by taking a subset of the vertices and discarding any edges that do not have both source and target node as part of the subset. You can also pass a function to filter vertices before the sampling is applied to have some control over the reduction.
It is advised to choose small samples first because the graph layout algorithm and the SVG drawing can be quite slow for huge graphs.
showEdgeSample[VD, ED](graph: Graph[VD, ED],
sampleSize: Int = 20,
edgeFilter: (Edge[ED]) => Boolean =
(edge: Edge[ED]) => true)Plots a sample of the given GraphX graph based on the edge set. DDS will sample the graph by taking a subset of the edges and discarding any vertices that do not appear as either source or target in the subset. You can also pass a function to filter edges before the sampling is applied to have some control over the reduction.
It is advised to choose small samples first because the graph layout algorithm and the SVG drawing can be quite slow for huge graphs.
connectedComponents[VD, ED](graph: graphx.Graph[VD, ED])Plots the number of nodes and the number of edges for each connected component present in the given graph.
To quickly get started with Spark and DDS, you can load one of the available example data sets either as an RDD of case classes or an RDD with a schema.
To access a data set you need to pass your Spark context (sc). If you want to apply a schema, you also need to pass a SQL context (sql). You may also provide them as implicits.
// RDD of case classes
val golf = de.frosner.dds.datasets.golf(sc)// RDD of Rows having a schema
val golf = de.frosner.dds.datasets.golf(sc, sql)// RDD of case classes
val flights = de.frosner.dds.datasets.flights(sc)// RDD of Rows having a schema
val flights = de.frosner.dds.datasets.flights(sc, sql)DDS comes with a set of interactive visualizations at the front-end side. The following sections explains only the visualizations that are truly interactive, i.e. the user can modify it by clicking and pressing buttons. Simple visualizations like tables or line charts are not covered here.
Tabular data is displayed in an interactive grid. The table contents can be sorted by clicking on the column header of the attribute to sort by. Each element is assigned an ID which links the contents of the grid with the accompanying plot (e.g. parallel coordinates).
If the table has many entries, it will be paginated. You can find the controls for pagination in the menu bar above the grid.
The parallel coordinates plot is a visualization technique to explore high dimensional data. Instead of drawing the axes orthogonally like in a 2D scatter plot, they are drawn in a parallel fashion. One row / data point corresponds to a polyline through all the axes. DDS currently supports two interactions with the parallel coordinates plot: Axis reordering and filtering. DDS offers parallel coordinates for all tabular data.
To reorder the axes, drag one axis on its label to a different position. This can be helpful to detect patterns like correlations or clusters in the data.
To change the ordering of the values on the axis, double click on the axis label.
To hide / show the ticks labels, press the 
button in the top right corner.
You can filter the values by selecting a range in one of the dimensions. Just click and span a filter region on an axis. DDS supports filters on multiple dimensions simultaneously. To change the filter just move it around or change its size. To delete a filter, just click on a different part of the axis that is not in range of the filter.
You can dynamically color the polylines in the parallel coordinates plot based on one dimension. To select the dimension to use for color coding, just click on the small grey circle above the axis. If the attribute is numerical, a linear scale from orange to red will be used. Otherwise, a multi-color scale will be used that does not imply any ordering.
When visualizing data in a scatter plot, you can choose whether to apply some random noise (jitter) on non-numerical axes. Toggle jitter by clicking on the 
/ 
button in the top right corner.
When displaying a graph in DDS, you can choose to hide / show edge and vertex labels. Toggle the visibility of them using the navigations buttons in the top right corner.
Additionally, you can choose between drawing directed and undirected edges.
When visualizing matrices as heat maps, it sometimes makes sense to try different color scales. As of today, DDS offers one two-color scale and one three-color scale. You can select the corresponding scale by clicking the colored buttons in the header menu.
It is also possible to customize the range of the color scale (min, max). For example, it makes sense to use a three color scale and (-1, 1) range when looking at a correlation matrix. Specify min and max values using the two input fields labeled "z", residing in the header menu.
DDS currently uses the Apache log4j logger which is also used by Spark. So you can configure the logging in the same way you configure logging in Spark.