Ideas for double bracket '[[' functionality

[karoliskoncevicius]

This issue is dedicated to gathering ideas for the implementation of [[ method in 'annmatrix'.

'annmatrix' tries to behave just as a regular matrix across every possible method. Therefore it has little wiggle-room for adding new functionality. Few of such freebies were @ and $ methods. 'annmatrix' was able to use them because in R neither @ nor $ do anything when called on a regular matrix.

Double bracket subsetting [[ is another such method. Currently in R for a regular matrix [[ only works when selecting single elements by passing a single index as an input. If this method is to be rewritten 'annmatrix' must preserve this functionality. However all the cases where the input is not a single number can be adjusted.

One idea about possible use case for [[ is "internal" subsetting. Instead of writing:

X <- X[X@chr == "chr1", X$diagnosis == "case"]

It would allow to safely write:

X <- X[[chr == "chr1", diagnosis == "case"]]

Might be useful, specially in cases with long annmatrix variable names.