How to copy a dataframe column within the same dataframe?

General Usage
1

Hi,

I would like to copy (not a view) a column of dataframe inside the same dataframe.

E.g. to have:

julia> df = DataFrame(A=1:4, B=["A", "B", "C", "D"])
4×2 DataFrame
 Row │ A      B      
     │ Int64  String 
─────┼───────────────
   1 │     1  A
   2 │     2  B
   3 │     3  C
   4 │     4  D

into, let’s say the “:new_col” containing the same elements as “:A”.
I’ve tried using

insertcols!(df, 3, copy(df.A), :new_col)

and some variants without success…

2

Do you mean this?

julia> df = DataFrame(A=1:4, B=["A", "B", "C", "D"])
4×2 DataFrame
 Row │ A      B
     │ Int64  String
─────┼───────────────
   1 │     1  A
   2 │     2  B
   3 │     3  C
   4 │     4  D

julia> df.b_again = copy(df.B);

julia> df.b_again[2] = "E";

julia> df
4×3 DataFrame
 Row │ A      B       b_again
     │ Int64  String  String
─────┼────────────────────────
   1 │     1  A       A
   2 │     2  B       E
   3 │     3  C       C
   4 │     4  D       D
2 Likes
3

Wonderful !
Thanks !

4

You could write:

insertcols!(df, 3, :new_col => df.A)

which in this case is the same as:

insertcols!(df, :new_col => df.A)
1 Like
5

Also consider using the following syntaxes:

julia> df = DataFrame(A=1:4, B=["A", "B", "C", "D"])
4×2 DataFrame
 Row │ A      B      
     │ Int64  String 
─────┼───────────────
   1 │     1  A
   2 │     2  B
   3 │     3  C
   4 │     4  D

julia> df[!, :C] = df.A
4-element Vector{Int64}:
 1
 2
 3
 4



julia> df
4×3 DataFrame
 Row │ A      B       C     
     │ Int64  String  Int64 
─────┼──────────────────────
   1 │     1  A           1
   2 │     2  B           2
   3 │     3  C           3
   4 │     4  D           4


julia> df.C[3]
3

julia> df.C[3] = 33
33

julia> df
4×3 DataFrame
 Row │ A      B       C     
     │ Int64  String  Int64
─────┼──────────────────────
   1 │     1  A           1
   2 │     2  B           2
   3 │    33  C          33
   4 │     4  D           4

julia> df[:, :D] = df.A
4-element Vector{Int64}:
  1
  2
 33
  4

julia> df.D[3]=3
3

julia> df
4×4 DataFrame
 Row │ A      B       C      D     
     │ Int64  String  Int64  Int64
─────┼─────────────────────────────
   1 │     1  A           1      1
   2 │     2  B           2      2
   3 │    33  C          33      3
   4 │     4  D           4      4
2 Likes