Possible issue with `fill` in `fread`

[mrdwab]

It's exciting to see that fread has gained some features that were previously slated as not-likely-to-be-implemented, for instance fill.

However, it seems like fread(..., fill = TRUE) is not happy when the first line is shorter than the longest row.

Using 1.9.7, obviously:

library(data.table)
packageVersion("data.table")
# [1] ‘1.9.7’

Simplest demonstration:

fread("1,a,b\n2", fill = TRUE)
#    V1 V2 V3
#1:  1  a  b
#2:  2      

fread("2\n1,a,b", fill = TRUE)
# Error in fread(paste(invec, collapse = "\n"), ...) : 
#   Unexpected character ending field 1 of line 1: 2
#1,a,

fread("v1,v2,v3\n2\n1,a,b", fill = TRUE)
#    v1 v2 v3
#1:  2      
#2:  1  a  b

Notice that by adding the column names in to the dataset itself, there is no problem with a shorter first row. So, I thought that using the col.names argument would help out in a situation like this. Unfortunately, it doesn't.

fread("2\n1,a,b", fill = TRUE, col.names = paste0("V", 1:3))
# Error in fread("2\n1,a,b", fill = TRUE, col.names = paste0("V", 1:3)) : 
#   Unexpected character ending field 1 of line 1: 2
#1,a,

Hope this is enough information to reproduce the behavior on your side too. Wanted to keep the samples simple :-)

[arunsrinivasan]

Just back from vacation. Thanks @mrdwab.