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FR: in colClasses of fread, allow column names not present in actual table #1602

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FR: in colClasses of fread, allow column names not present in actual table#1602
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enhancementfread

Description

@aushev
aushev
opened on Mar 19, 2016

I often need to read multiple tables that share some (but not all) columns which would be passed to colClasses. It would be then convenient to make one vector with all those column names, i.e. instead of

chrcols1 <- c('colA', 'colB')
dt1 <- fread(file1, colClasses=list(character=chrcols1))
chrcols2 <- c('colA', 'colC')
dt2 <- fread(file2, colClasses=list(character=chrcols2))
# etc

use

chrcolsAll <- c('colA', 'colB', 'colC')
dt1 <- fread(file1, colClasses=list(character=chrcolsAll))
dt2 <- fread(file2, colClasses=list(character=chrcolsAll))

Right now this is not allowed ( "Column name '%s' in colClasses[[%d]] not found" ) but instead of throwing an error we could just exclude those column names from further processing.

Activity

  1. aushev
    changed the title [-]FR: in colClasses, allow column names not found in actual table[/-] [+]FR: in colClasses of fread, allow column names not present in actual table[/+] on Mar 20, 2016
  2. jangorecki
    added
    fread
    on Mar 5, 2017
  3. st-pasha
    added
    enhancement
    on Jul 6, 2017

  4. gdmcdonald commented on Jul 24, 2019

    @gdmcdonald
    gdmcdonald
    on Jul 24, 2019

    This would be a great feature!

  5. MichaelChirico commented on Jul 24, 2019

    @MichaelChirico
    MichaelChirico
    on Jul 24, 2019
    Member

    In current dev, this is a warning (DTWARN), whereas in the linked commit it was an error (STOP).

    Is a warning too strict here? The idea is to relegate it to verbose output only? Or can we close this?

  6. gdmcdonald commented on Jul 25, 2019

    @gdmcdonald
    gdmcdonald
    on Jul 25, 2019

    Ahhhhh yes the current dev solves all my problems! Thankyou

  7. ben-schwen commented on Oct 17, 2025

    @ben-schwen
    ben-schwen
    on Oct 17, 2025
    Member

    Current version implements this and warning seems like the right choice. Closing here, but feel free to reopen if the issue rearises or you feel that a warning is too much.

  8. ben-schwen
    closed this as completedon Oct 17, 2025
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