Flysystem/CSV filter a subset of columns

Question

Is it possible to filter a subset of columns of a CSV with Flysystem CSV?

I know that you can use AbstractCsv::addFilter(callable $callback) to add arbitrary filters, but I don't think you would use this to drop a column.

Answer 1

I solved this by getting an array of the column positions that I wanted to filter out. Then, by setting up a new CSV object to write to e.g.

$new = Writer::createFromFileObject(new \SplTempFileObject);

With the CSV to read from, I used the each method to iterate through its rows, building a new row using the column indexes built earlier on and inserting into the new CSV. Remember to return true; in the each method or it won't iterate.

$csv = $csv->newReader();
$csv->setOffset(1);
$csv->each(function ($row) use ($new) {
    ... do stuff to alter the row ...
    $new->insertOne($alteredRow)
});