bills.php

<?php

return [
    [
        'title' => 'Nubank',
        'amount' => 1455.73,
        'due_date' => new \DateTime('01-11-2016'),
        'tags' => [],
        'paid' => true,
    ],
    [
        'title' => 'Renner',
        'amount' => 124.75,
        'due_date' => new \DateTime('01-11-2016'),
        'tags' => ['clothes'],
    ],
    [
        'title' => 'Carro',
        'amount' => 613,
        'due_date' => new \DateTime('08-11-2016'),
        'tags' => [],
    ],
    [
        'title' => 'Aluguel',
        'amount' => 1324.88,
        'due_date' => new \DateTime('04-11-2016'),
        'bar_code' => '03399.21199 54400.000227 79886.201023 1 69680000132488',
        'tags' => ['friends'],
    ],
    [
        'title' => 'Condomínio',
        'amount' => 612.83,
        'due_date' => new \DateTime('10-11-2016'),
        'bar_code' => '08591.06098 10014.010408 00007.535016 2 69740000061284',
        'tags' => ['friends'],
    ],
    [
        'title' => 'Internet',
        'amount' => 104.90,
        'due_date' => new \DateTime('07-11-2016'),
        'tags' => ['friends'],
    ],
    [
        'title' => 'Luz',
        'amount' => 225.69,
        'bar_code' => '836800000025 256901620003 001010201620 348298677090',
        'due_date' => new \DateTime('27-10-2016'),
        'tags' => ['friends'],
    ],
];

composer.json

{
    "require": {
        "prelude/prelude": "dev-master"
    },
    "repositories": [
        {
            "type": "vcs",
            "url":  "[email protected]:sergiors/prelude.git"
        }
    ]
}

index.php

<?php

use const Prelude\{_, not, get, divide, sum};
use function Prelude\{placeholder, pipe, filter, map, get, find, equals, join};

require __DIR__.'/vendor/autoload.php';

$bills = require __DIR__.'/bills.php';

$findFriendsTag = pipe(placeholder(get, _, 'tags', []), find(equals('friends')));

$filterFriends = filter($findFriendsTag);

$filterMy = filter(pipe($findFriendsTag, not));

$filterPedding = filter(pipe(placeholder(get, _, 'paid', false), equals(false)));

$sumAmount = pipe(map(placeholder(get, _, 'amount', 0)), sum);

$fmtPerLine = map(function (array $bill) {
    return get($bill, 'title', '').' - '.get($bill, 'amount', 0.0);
});

$fmtBills = pipe($fmtPerLine, join("\n"));

$expensesFriends = pipe($filterFriends, $sumAmount);

$expensesPerFriend = pipe($expensesFriends, placeholder(divide, _, 3));

$myExpensesSum = pipe($filterMy, $sumAmount);

echo pipe($filterMy, $filterPedding, $fmtBills)($bills), "\n",
    pipe($filterPedding, $myExpensesSum)($bills), "\n";

echo pipe($filterFriends, $fmtBills)($bills), "\n",
    $expensesFriends($bills), "\n",
    $expensesPerFriend($bills), "\n";

/*
Renner - 124.750000
Carro - 613.000000
737.75
Aluguel - 1324.880000
Condomínio - 612.830000
Internet - 104.900000
Luz - 225.690000
2268.3
756.1
*/