Process CSV datasets efficiently

This is just a collection of functions to process CSV (and other) data structures. The functions are designed in such a way that they can be combined to build processing pipelines. All functions return Generators to ensure that big data sets can be processed without having everything in memory.

The concepts are inspired by lazy functional programming which is very cool :-)

Example (from example.php)

// don't worry, there is also a composer autoloader
// defined
include './csv_functions.php';

use Ckr\CSV as C;

// First, we want to filter the products,
// so we only have the healthy ones...
$filterHealthy = C\buildFilter(
    function (array $row) {
        return $row['is_healthy'] > 5;
    }
);

// We're not interested in the inventory, so
// we select only the other fields
$selectFields = C\buildSelect(
    ['id', 'product', 'price']
);

// Unfortunately, this are not the real prices,
// we also have to add taxes...
$mapAddTaxes = C\buildMap(
    function (array $row) {
        $priceWithTax = floatval($row['price']) * 1.20;
        $row['price_incl_tax'] = $priceWithTax;
        return $row;
    }
);

// Now, lets combine this processing stages to
// a pipeline
$pipeline = C\combineStages(
    $filterHealthy,
    $selectFields,
    $mapAddTaxes
);

// Ehm..., and we also need to have nice string representation
// of the products.
// No problem, we can combine the
// current pipeline -- which is itself a processing stage --
// with another processor
$mapStringField = C\buildMap(
    function (array $row) {
        $str = sprintf(
            '%s (%d) is healthy product and costs only $%s',
            $row['product'],
            intval($row['id']),
            number_format($row['price_incl_tax'], 2)
        );
        $row['as_text'] = $str;
        return $row;
    }
);

// build the new pipeline. Note, that we also need to
// map the "primitive" indexed arrays to associative
// arrays. This is done by the 'toAssoc' function
$newPipeline = C\combineStages(
    'Ckr\\CSV\\toAssoc',
    $pipeline,
    $mapStringField
);

// Now we want to read the csv file, process each row
// and write the result to the output
$input = './example.csv';

// Note that this is still a generator, not the actual
// data. The input file has not yet been read!
$data = $newPipeline(C\readFromFile($input));

// Then we write everything to stdout
$outStream = fopen('php://stdout', 'wb');
C\writeToResource($data, $outStream);