assign new columns to datatable

Question

How do I assign new columns to a datatable?

Tried this:

DT1 = dt.Frame(A = range(5))
DT1['B'] = [1, 2, 3, 4, 5]

But getting

ValueError: The LHS of the replacement has 1 columns, while the RHS has 5 replacement expressions

Answer 1

With DT[col] = ... syntax you can assign single-column datatable Frames, or numpy arrays, or pandas DataFrames or Series. In your example, you just need to wrap the rhs into a Frame:

>>> DT1['B'] = dt.Frame([1, 2, 3, 4, 5])
>>> DT1
   |     A      B
   | int32  int32
-- + -----  -----
 0 |     0      1
 1 |     1      2
 2 |     2      3
 3 |     3      4
 4 |     4      5
[5 rows x 2 columns]