Add a Column of Random Booleans

Question

Given a table t, add a new column d that contains a random boolean for every row.

For example:

t:([] sym:`A`B`C; price:120.5 151.2 175.0)

Solution

update d:(count t)?0b from `t

Explanation

(count t)?0b generates one random boolean per row of t — count t gives the number of rows needed, and ? with a boolean atom (0b) on the right draws that many random 0b/1b values.

update d:... from tadds the result as a new columnd. Passing the table name as a symbol (`` t ``) makes the update happen in place, rather than returning a new table that would need to be reassigned.