Lulu Arrays — Mapping & Transforming

Introduction

If you have imported the lulu.Array class as

local Array = require 'lulu.Array'

Then, you have access to the following methods:

Array:map(fun,...)
Returns a new Array, which results from applying fun to each value in self.

Array:transform(fun,...)
Transform an Array in place by applying fun to each top-level value. This method returns the transformed self and is ready for further processing.

Array:map

Classic “functional” method that creates a new table by applying fun to each value in self.

In this implementation, the function also passes any extra ... arguments in the call to Array:map(fun,...).

If the returned Array is the result, then for each index k, we set:

result[k] = fun(self[k],...)

Of course, fun may ignore those extra arguments entirely, and Lua is happy to call a function with multiple arguments, even if it only uses the first one.

Example:

local lower = Array{'warning', 'notice', 'hint'}
local upper = lower:map(string.upper)
1putln("lower: %t", lower)
putln("upper: %t", upper)

1

The examples on this page use putln from lulu.scribe for formatted printing.

Output:

lower: ["warning", "notice", "hint"]
1upper: ["WARNING", "NOTICE", "HINT"]

1

We mapped the Lua standard string.upper(...) method over every value in the lower array.

Array:transform

This method is like map above except that it works in place, so for each index k, we set:

self[k] = fun(self[k],...)

Example:

local admonitions = Array{'warning', 'notice', 'hint'}
putln("admonitions: %t", admonitions)
admonitions:transform(string.upper)
putln("admonitions: %t", admonitions)

Output:

admonitions: ["warning", "notice", "hint"]
admonitions: ["WARNING", "NOTICE", "HINT"]

See Also

lulu.callable