Check dynamic matrix indexing in R code. Sometimes, an expression like m[i:j, ] will return a matrix (when i != j) and otherwise a vector. This is a source of bugs in much of my R code. m[i:j, , drop=FALSE] explicitly disables this behavior. This gist contains R code to check your R code for matrix indexing operations that don't have drop= speci…

checkMatrix.R

library(codetools)

addMatrixHandler <- function(fn) {
  addCollectUsageHandler('[', 'base', fn)
}

myMatrixHandler <- function(e, w) {
  w$enterGlobal("function", "[", e, w)
  if (length(e) > 3 && !('drop' %in% names(e))) {
    simple <- sapply(dropMissings(e[-(1:2)]), function(a) {
      length(a) == 1 && !is.symbol(a) &&
        (is.numeric(a[[1]]) || is.character(a[[1]]))
    })
    if(!all(simple)) {
      w$signal(
        paste("Indexing a matrix, but not specifying 'drop' in",
          pasteExpr(e)),
        w)
    }
  }
  for (a in dropMissings(e[-1])) walkCode(a, w)
}

env <- getNamespace("codetools")
environment(addMatrixHandler) <- env
environment(myMatrixHandler) <- env

addMatrixHandler(myMatrixHandler)

# To check a single function:
# checkUsage(fn)
# To check a package:
# library(pkgName); checkUsagePackage('pkgName')