[Bug]merge is now merging on col order instead of name

[ChristK]

Please see example below

require(data.table) #latest github version

DT1 <- data.table(sex = rep(1:2, 5),
                  group = rep(letters[1:5], 2),
                  V1 = 1:10)

DT2 <- data.table(group = rep(letters[1:5], 2), # note the different order
                  sex = rep(1:2, 5),
                  V2 = 1:10)

merge(
  DT1, DT2, by = c("sex", "group")
)

# WRONG! sex should be numbers and group letters
#   sex group V1 V2
#1:   a     1  1  1
#2:   a     2  6  6
#3:   b     1  7  7
#4:   b     2  2  2
#5:   c     1  3  3
#6:   c     2  8  8
#7:   d     1  9  9
#8:   d     2  4  4
#9:   e     1  5  5
#10:   e     2 10 10

 sessionInfo()

#R version 3.2.2 (2015-08-14)
#Platform: x86_64-pc-linux-gnu (64-bit)
#Running under: Ubuntu 14.04.2 LTS
#
#locale:
# [1] LC_CTYPE=en_GB.UTF-8       LC_NUMERIC=C              
# [3] LC_TIME=en_GB.UTF-8        LC_COLLATE=en_GB.UTF-8    
# [5] LC_MONETARY=en_GB.UTF-8    LC_MESSAGES=en_GB.UTF-8   
# [7] LC_PAPER=en_GB.UTF-8       LC_NAME=C                 
# [9] LC_ADDRESS=C               LC_TELEPHONE=C            
#[11] LC_MEASUREMENT=en_GB.UTF-8 LC_IDENTIFICATION=C       

#attached base packages:
#[1] stats     graphics  grDevices utils     datasets 
#[6] methods   base     
#
#other attached packages:
#[1] data.table_1.9.5
#
#loaded via a namespace (and not attached):
#[1] tools_3.2.2  chron_2.3-47

The bug was introduced probably the last week. (Edited with simpler example)

[arunsrinivasan]

Thanks for the nice report. Fixed.

[ChristK]

Thank you!

It took me more time to report it than you to fix it 👍