built in compound operators: pick

pick:
    description:
        pick[n] input-seq
        randomly pick n elements from each superposition in the input sequence
        if n is greater than the size of the superposition, then only return size(superposition) elements
        if n is less than or equal 0, return the empty ket

    examples:
        -- randomly pick three elements from the given superposition:
        pick[3] (|one> + |two> + |three> + |four> + |five> + |six> + |seven>)
            |three> + |seven> + |four>

    see also:
        pick-elt, weighted-pick-elt