Julia DataFrame: shift a column by more rows

I am looking for a way how to shift DataFrame column by more rows.

Shifting by one row works fine:

df = DataFrame(A=[1,2,3,4], B=[9,8,7,6])

julia> transform(df, "A" => ShiftedArrays.lag => :A1)
4×3 DataFrame
 Row │ A      B      A1
     │ Int64  Int64  Int64?
─────┼───────────────────────
   1 │     1      9  missing
   2 │     2      8        1
   3 │     3      7        2
   4 │     4      6        3

But I am not able to find out how to transform the entire column with a function with more arguments, something like this (neither works):

transform(df, "A" => x -> ShiftedArrays.lag(x, 2) => :A1)

or

transform(df, ["A", 2] => f => :A1)

I hope there is a more suitable solution than using of for loop 🙂

>Solution :

You need additional parentheses around the lambda function:

transform(df, "A" => (x -> ShiftedArrays.lag(x, 2)) => :A1)

Result:
 Row │ A      B      A1      
     │ Int64  Int64  Int64?  
─────┼───────────────────────
   1 │     1      9  missing 
   2 │     2      8  missing 
   3 │     3      7        1
   4 │     4      6        2