fread header = "auto" works strange

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
35/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by reproducing the examples through fread with header = "auto", focusing on partially empty headers and character-only columns. Trace the header-detection entry point and existing tests for fread; done means the demonstrated inputs produce consistent, intended column names without changing the valid four-column case.

Written by the indexing model from the issue text.

Description

fread

It works strange for partially empty headers and only character columns.

fread("col1;col2;col3;col4;;;;;;;
aaaa;bbbb;cccc;dddd;;;;;;;")
#      V1   V2   V3   V4 V5 V6 V7 V8 V9 V10 V11
# 1: col1 col2 col3 col4 NA NA NA NA NA  NA  NA
# 2: aaaa bbbb cccc dddd NA NA NA NA NA  NA  NA

fread("col1;col2;col3;col4
aaaa;bbbb;cccc;dddd")
#    col1 col2 col3 col4
# 1: aaaa bbbb cccc dddd

fread("col1;col2;col3;col4;;;;;;;
aaaa;2;cccc;dddd;;;;;;;")
#    col1 col2 col3 col4 V5 V6 V7 V8 V9 V10 V11
# 1: aaaa    2 cccc dddd NA NA NA NA NA  NA  NA

Error is reproduced from 1.11.0

Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 7 x64 (build 7601) Service Pack 1

Matrix products: default

locale:
[1] LC_COLLATE=Russian_Russia.1251  LC_CTYPE=Russian_Russia.1251    LC_MONETARY=Russian_Russia.1251 LC_NUMERIC=C                    LC_TIME=Russian_Russia.1251    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.12.0 devtools_1.13.4  

loaded via a namespace (and not attached):
[1] compiler_3.4.3 tools_3.4.3    withr_2.1.1    yaml_2.1.16    memoise_1.1.0  digest_0.6.14 ```
Dominant language
R
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Merged PRs (30d)
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