LuaQ

Inspired by Linq

LuaQ is a set of functions for manipulating iterators in a similar fashion to the popular System.Linq library in dotnet.

Example

Include the library

local query = require('query')

Using queries

-- the identity property of queries
local q = query{ 1, 2, 3, 4 }

-- iterate through the query
for item in q.list() do
    print(item)
end
-- prints [1, 2, 3, 4]

-- shorthand for printing a query
q:print() -- prints [1, 2, 3, 4]

-- you can also create queries from other iterators
local q = query(query.range(1, 5))

q:print() -- [1, 2, 3, 4, 5]

Filtering

-- to filter a query pass a predicate to the where method
function isEven(value)
    return value % 2 == 0
end

local q = query{1, 2, 3, 4}:where(isEven)

q:print() -- [2, 4]

-- you may prefer to use anonymous functions
local q = query{1, 2, 3, 4}:where(function (v) return v % 2 == 0 end)

q:print() -- [2, 4]

-- you can also pass lambda strings such as this
local q = query{1, 2, 3, 4}:where('v -> v % 2 == 0')

q:print() -- [2, 4]

Transforming

-- to transform or select data from an item, use the select method
local q = query{1, 2, 3, 4}:select('v -> v * v')

q:print() -- [1, 4, 9, 16] 

-- you can continue to chain together operations
local q = query(query.range(1,10))
                :select('v -> v * v')
                :select('v -> tostring(v)')
                :where('s -> string.len(s) ~= 2')

q:print() -- [1, 4, 9, 100]                    

Enumeration

-- For most operations, each operation is applied once to each peice of data
local q = query{1, 2, 3, 4}
                :where(function (v)
                    print("First operation, " .. v)
                    return v == 3
                end)
                :select(function (v)
                    print("Second operation, " .. v)
                    return "(" .. v .. ")"
                end)

q:print()
-- output:
First operation, 1
First operation, 2
First operation, 3
Second operation, 3
(3) 
First operation, 4

Operations that return a new query execute only when they are enumerated. Other operations that return specific values or have to look all of the data to return the next item execute immediately.

Aggregate

-- sum a list using aggregate
local sum = query{1, 2, 3, 4}:aggregate('value, accumulator -> value + accumulator', 0)

print(sum) -- 10

local cat =  query{1, 2, 3, 4}:aggregate('value, accumulator -> value .. accumulator', '')

print(cat) -- 4321

First, FirstOrDefault, Single, etc

-- select first item
local q = query{1, 2, 3, 4}:first() -- 1

local q = query{1, 2, 3, 4}:first('v -> v > 10')
Error: No item matched predicate

local q = query{1, 2, 3, 4}:firstOrDefault('v -> v > 10') -- nil

local q = query{1, 2, 3, 4}:single('v -> v == 1') -- 1

local q = query{1, 2, 3, 4}:single()
Error: More than 1 item matched predicate

local q = query{1, 2, 3, 4}:single('v -> v < 2 or v > 3')
Error: More than 1 item matched predicate

local q = query{1, 2, 3, 4}:any() -- true

local q = query{1, 2, 3, 4}:any('v -> v > 10') -- false    

local q = query{1, 2, 3, 4}:contains(3) -- true

local q = query{1, 2, 3, 4}:contains("3") -- false

Skip, Take

local q = query{1, 2, 3, 4}:skip(1) -- [2, 3, 4]

local q = query{1, 2, 3, 4}:take(1) -- [1]
-- note, this query returns a query of length 1, not the number 1

local q = query{1, 2, 3, 4}:skip(1):take(1) -- [2, 3]

local q = query(query.range(1,10)):skip(2):take(1):skip(2):take(1) -- [3, 6]