Expr.when

Expr when(Expr a, Expr b) @safe

Selects between two branches by this BOOLEAN expression (the eager when kernel: promoted branches; length-1 operands broadcast to the common height at evaluation).

Parameters

`a`	the branch selected where this mask is `true`
`b`	the branch selected where this mask is `false`

Returns

the conditional expression (a member rather than a

free function so it never conflicts with the eager ddn.df.compute.when under the package import).

Throws

DataFrameException when the mask or a branch is an

aggregate.