[R] read columns of quoted numbers as factors

[james hirschorn]

Suppose I have a data file (possibly with a huge number of columns), where the 
columns with factors are coded as "1", "2", "3", etc ... The default behavior of 
read.table is to convert these columns to integer vectors. 

Is there a way to get read.table to recognize that columns of quoted numbers 
represent factors (while unquoted numbers are interpreted as integers), without 
explicitly setting them with colClasses ?