julia> df = DataFrame(x=rand(1:3, 10), y=rand(1:3, 10), z=rand(10))
10×3 DataFrame
 Row │ x      y      z
     │ Int64  Int64  Float64
─────┼────────────────────────
   1 │     3      2  0.975774
   2 │     2      2  0.437708
   3 │     1      3  0.683004
   4 │     1      1  0.998265
   5 │     3      2  0.744942
   6 │     2      3  0.735679
   7 │     1      3  0.337943
   8 │     3      1  0.471394
   9 │     3      2  0.477417
  10 │     2      3  0.811261

julia> unstack(df, :x, :y, :z, combine=length)
3×4 DataFrame
 Row │ x      2        3        1
     │ Int64  Int64?   Int64?   Int64?
─────┼──────────────────────────────────
   1 │     3        3  missing        1
   2 │     2        1        2  missing
   3 │     1  missing        2        1