Duplicate Each Element in a List

Question

Given:

l:`a`b`c`c`d

Duplicate each element in the list to produce:

`a`a`b`b`c`c`c`c`d`d

Solution

raze (2#) each l

Alternative Solution

raze l,'l

Alternative Solution

raze 2#/:l

Explanation

(2#) each l

applies the take operator 2# independently to every symbol in l, turning each single symbol into a 2-item list containing it twice:

a a
b b
c c
c c
d d

raze then flattens that list of lists back into a single flat list.

The alternatives reach the same result with related iterators: l,'l uses each-both (') to join l with itself item by item, and 2#/:l uses each-right (/:) to take 2 of each item on the right. All three demonstrate how closely each, each-both, and each-right are related — they differ only in which side of the function holds the list being iterated over.