iter

Map, filter and transform lazy iterators.

iter offers the familiar map(), filter(), etc but with a twist: rather than transforming tables, iter transforms the iterator. Transformations are lazy and no work is done until iterator is consumed (usually with a for loop). This is faster and more memory efficient, since items are transformed one-by-one as iterator is consumed and no interim tables are created.

Example

-- Import iter functions
local iter = require('iter')
local map = iter.map
local filter = iter.filter
local values = iter.values

-- Import an enormous table
local very_large_table = require('verylargetable.lua')

-- Create an iterator function for table values
local v = values(very_large_table)

-- Filter and transform values. At each step, a new iterator function is
-- returned for the transformed values. No intermediate tables are created.
local odd_values = filter(is_odd, v)
local values_greater_than_2 = filter(is_greater_than_2, odd_values)
local square_roots = map(square_root, values_greater_than_2)

-- Consume our final iterator. This is when all the work happens.
for v in square_roots do
  print(v)
end

Documentation

Documentation and annotated source.

Installation

Using Luarocks:

luarocks install iter

Then in your Lua file, you can:

local iter = require('iter')

That's it!