select.md

select, reject

Filters a collection

"select" and "reject" are the 'block-oriented' children of "filter" and "filter-out" respectively.

select [ 1, 2, 3, 4, 5 ]
  = (elt % 2) 1

# f.ret --> [ 1, 3, 5 ]

Note that the equivalent "filter" is:

filter [ 1, 2, 3, 4, 5 ]
  def x
    = (x % 2) 1

The blocks understand elt (the current element), idx (the current zero-based index), and key (the current key for an object/hash).

with objects (hashes)

select { a: 'A', b: 'B', c: 'C', d: 'D' }
  key == 'a' or val == 'C' or idx == 3

# f.ret --> { 'a' => 'A', 'c' => 'C', 'd' => 'D' }

reject

"reject" is the negative of "select".

reject [ 1, 2, 3, 4, 5 ]
  (elt % 2) == 0

# f.ret --> [ 1, 3, 5 ]

iterating blocks

Iterating blocks are given 3 to 4 local variables.

A block iterating over an array will receive elt (the current element of the iteration), idx (the zero-based index of the current element), and len (the length of the array).

A block iterating over an object will receive key (the current string key), val (the current value), idx (the zero-based index of the current key/val), and len (the length of the object).

see also

filter, map, reject, and collect.

• source
• select spec