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nrows=0 interferes with proper sep detection #2747

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nrows=0 interferes with proper sep detection#2747
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bugfread
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1.12.0

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@st-pasha
st-pasha
opened on Apr 13, 2018

(even if sep is given explicitly):

> fread("A,B,C\n1,2,3\n3,4,5\n0,0,0\n", nrows=0)
Empty data.table (0 rows) of 1 col: A,B,C
> fread("A,B,C\n1,2,3\n3,4,5\n0,0,100\n", nrows=0, sep=',')
Empty data.table (0 rows) of 1 col: A,B,C

Expected result: a 0 rows x 3 columns data.table with columns "A", "B", and "C"

Also, documentation says

nrows=0 returns the column names
and typed empty columns determined by the large sample;
useful for a dry run of a large file or to quickly check
format consistency of a set of files before starting to read
any of them.

As far as I understand, this is no longer accurate.

Activity

  1. st-pasha
    added
    bug
    fread
    on Apr 13, 2018
  2. st-pasha
    added this to the milestone on Apr 13, 2018
  3. mattdowle
    modified the milestones: v1.11.0, on Apr 29, 2018

  4. mattdowle commented on Jan 11, 2019

    @mattdowle
    mattdowle
    on Jan 11, 2019
    Member

    Not sure when this was fixed, but it looks fixed now. Will add tests.

    > fread("A,B,C\n1,2,3\n3,4,5\n0,0,0\n", nrows=0)
Empty data.table (0 rows) of 3 cols: A,B,C
> fread("A,B,C\n1,2,3\n3,4,5\n0,0,100\n", nrows=0, sep=',')
Empty data.table (0 rows) of 3 cols: A,B,C
  5. mattdowle
    closed this as completedin f84bf07on Jan 11, 2019
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