dfr std for expression

Creates a std expression for an aggregation of std value from columns in a dataframe

Signature

> dfr std

Input/output types:

input	output
any	any

Examples

Std value from columns in a dataframe

> [[a b]; [6 2] [4 2] [2 2]] | dfr into-df | dfr std
╭───┬──────┬──────╮
│ # │  a   │  b   │
├───┼──────┼──────┤
│ 0 │ 2.00 │ 0.00 │
╰───┴──────┴──────╯

Std aggregation for a group-by

> [[a b]; [one 2] [one 2] [two 1] [two 1]]
    | dfr into-df
    | dfr group-by a
    | dfr agg (dfr col b | dfr std)
╭───┬─────┬──────╮
│ # │  a  │  b   │
├───┼─────┼──────┤
│ 0 │ one │ 0.00 │
│ 1 │ two │ 0.00 │
╰───┴─────┴──────╯

Tips: Dataframe commands were not shipped in the official binaries by default, you have to build it with --features=dataframe flag