Select multiple columns in data table by their numeric indices

Question

How can we select multiple columns using a vector of their numeric indices  position  in data table   This is how we would do with a data frame   df  lt - data frame a   1  b   2  c   3  df    2 3      b c   1 2 3

User · Answer

From v1 10 2 onwards  you can also use     dt  lt - data table a 1 2  b 2 3  c 3 4   keep cols   c  a    c    dt     keep cols

User · Answer

If you want to use column names to select the columns  simply use      which is an alias for list     library data table  dt  lt - data table a   1 2  b   2 3  c   3 4  dt      b  c     select the columns b and c   Result       b c   1  2 3   2  3 4

User · Answer

It s a bit verbose  but i ve gotten used to using the hidden  SD variable    b lt -data table a 1 b 2 c 3 d 4  b   SD  SDcols c 1 2     It s a bit of a hassle  but you don t lose out on other data table features  I don t think   so you should still be able to use other important functions like join tables etc

User · Answer

For versions of data table  gt   1 9 8  the following all just work   library data table  dt  lt - data table a   1  b   2  c   3     select single column by index dt   2       b   1  2    select multiple columns by index dt   2 3       b c   1  2 3    select single column by name dt    a        a   1  1    select multiple columns by name dt   c  a    b         a b   1  1 2     For versions of data table  lt  1 9 8  for which numerical column selection required the use of with   FALSE   see this previous version of this answer  See also NEWS on  v1 9 8  POTENTIALLY BREAKING CHANGES  point 3

User · Answer

Tom  thank you very much for pointing out this solution   It works great for me    I was looking for a way to just exclude one column from printing and from the example above  To exclude the second column you can do something like this  library data table  dt  lt - data table a 1 2  b 2 3  c 3 4  dt   SD  SDcols -2  dt   SD  SDcols c 1 3

[r] Select multiple columns in data.table by their numeric indices

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