``lua
local roselect = require(path.to.roselect)
local createSelector = roselect.createSelector
local reduce = roselect.reduce

local function shopItemsSelector(state)
return state.shop.items
end

local function taxPercentSelector(state)
return state.shop.taxPercent
end

local subtotalSelector = createSelector(
shopItemsSelector,
function(items)
return reduce(items, function(acc, item)
return acc + item.value
end, 0)
end
)

local taxSelector = createSelector(
subtotalSelector,
taxPercentSelector,
function(subtotal, taxPercent)
return subtotal * (taxPercent / 100)
end
)

local totalSelector = createSelector(
subtotalSelector,
taxSelector,
function(subtotal, tax)
return { total = subtotal + tax }
end
)

local exampleState = {
shop = {
taxPercent = 8,
items = {
{ name = "apple", value = 1.20 },
{ name = "orange", value = 0.95 }
}
}
}

print(subtotalSelector(exampleState)) -- 2.15
print(taxSelector(exampleState)) -- 0.172
print(totalSelector(exampleState)) -- { total = 2.322 }
`


`ts
import { createSelector } from "@rbxts/roselect";

interface State {
shop: {
taxPercent: number;
items: { name: string; value: number; }[];
}
}

const shopItemsSelector = (state: State) => state.shop.items;
const taxPercentSelector = (state: State) => state.shop.taxPercent;

const subtotalSelector = createSelector(
shopItemsSelector,
items => items.reduce((acc, item) => acc + item.value, 0)
);

const taxSelector = createSelector(
subtotalSelector,
taxPercentSelector,
(subtotal, taxPercent) => subtotal * (taxPercent / 100)
);

export const totalSelector = createSelector(
subtotalSelector,
taxSelector,
(subtotal, tax) => ({ total: subtotal + tax })
);

const exampleState = identity({
shop: {
taxPercent: 8,
items: [
{ name: 'apple', value: 1.20 },
{ name: 'orange', value: 0.95 },
]
}
});

print(subtotalSelector(exampleState)); // 2.15
print(taxSelector(exampleState)); // 0.172
print(totalSelector(exampleState)); // { total: 2.322 }
`


`lua
local function getVisibilityFilter(state)
return state.visibilityFilter
end

local function getTodos(state)
return state.todos
end

local function getKeyword(state)
return state.keyword
end

local getVisibleTodos = createSelector(
{ getVisibilityFilter, getTodos },
function(visibilityFilter, todos)
if visibilityFilter == "SHOW_ALL" then
return todos
elseif visibilityFilter == "SHOW_COMPLETED" then
local newTodos = {}

for k, todo in pairs(todos) do
if todo.completed then
newTodos[k] = todo
end
end

return newTodos
elseif visibilityFilter == "SHOW_ACTIVE" then
local newTodos = {}

for k, todo in pairs(todos) do
if not todo.completed then
newTodos[k] = todo
end
end

return newTodos
end
end
)

local getVisibleTodosFilteredByKeyword = createSelector(
{ getVisibleTodos, getKeyword },
function(visibleTodos, keyword)
local newTodos = {}

for k, todo in pairs(visibleTodos) do
if todo.text:find(keyword) then
newTodos[k] = todo
end
end

return newTodos
end
)

return {
getVisibleTodos = getVisibleTodos
}
`

`ts
const getVisibilityFilter = (state: State) => state.visibilityFilter;
const getTodos = (state: State) => state.todos;
const getKeyword = (state: State) => state.keyword;

export const getVisibleTodos = createSelector(
[ getVisibilityFilter, getTodos ],
(visibilityFilter, todos) => {
switch (visibilityFilter) {
case "SHOW_ALL":
return todos;
case "SHOW_COMPLETED":
return todos.filter(t => t.completed);
case "SHOW_ACTIVE":
return todos.filter(t => !t.completed);
}
}
);

const getVisibleTodosFilteredByKeyword = createSelector(
[ getVisibleTodos, getKeyword ],
(visibleTodos, keyword) => visibleTodos.filter(
todo => todo.text.includes(keyword)
)
);
``