(This has been discussed on R-help [1])


The colClasses argument to read.table needs to be in the order of
the columns even when it is named if it is as long as there are
columns.  This is not in the documentation.

Here is a MWE:

--8<---------------cut here---------------start------------->8---
kkk <- c("a\tb",
         "3.14\tx")

## works without specifying colClasses
read.table(textConnection(kkk),
           sep="\t",
           header = TRUE)

cclasses=c(b="character",
           a="numeric")

## works with short/named colClasses
read.table(textConnection(kkk),
           sep="\t",
           header = TRUE,
           colClasses = cclasses[1])

## works with ordered colClasses
read.table(textConnection(kkk),
           sep="\t",
           header = TRUE,
           colClasses = cclasses[order(names(cclasses))])

## error
read.table(textConnection(kkk),
           sep="\t",
           header = TRUE,
           colClasses = cclasses)
--8<---------------cut here---------------end--------------->8---



In the thread on R-help Henrik Bengtsson provided a patch which I
inline here:


[HB-X201]{hb}: svn diff src\library\utils\R\readtable.R
Index: src/library/utils/R/readtable.R
===================================================================
--- src/library/utils/R/readtable.R     (revision 68642)
+++ src/library/utils/R/readtable.R     (working copy)
@@ -139,7 +139,7 @@
     if (rlabp) col.names <- c("row.names", col.names)

     nmColClasses <- names(colClasses)
-    if(length(colClasses) < cols)
+    if(length(colClasses) <= cols)
         if(is.null(nmColClasses)) {
             colClasses <- rep_len(colClasses, cols)
         } else {



Thanks,
Andreas

[1] http://permalink.gmane.org/gmane.comp.lang.r.general/321919