Merging CSV lines where column value is the same - php

Question

I have a big CSV file with about 30 columns and 2.5K rows.
Some of the rows have exactly the same values except some columns.
I would like to merge those alike and concatenate with a comma between the values of the columns that are not the same.
Small example:
id name age kid
1 Tom 40 John
1 Tom 40 Roger
---merged becomes---
1 Tom 40 John, Roger
I can do this with PHP using lots and lots of fors and ifs but I am hoping that there's a more elegant and fast way.

Answer 1

This is a great beginner question for a common programming problem. What you'll want to do is a two step approach. First, parse the CSV into a data structure that you can easily modify, then loop over that structure and generate a new array that matches the output.
<?php
// Parse CSV into rows like:
$rows = array(
array(
'id' => 1,
'name' => 'Tom',
'age' => 50,
'kid' => 'John'
),
array(
'id' => 1,
'name' => 'Tom',
'age' => 50,
'kid' => 'Roger'
),
array(
'id' => 2,
'name' => 'Pete',
'age' => 40,
'kid' => 'Pete Jr.'
),
);
// Array for output
$concatenated = array();
// Key to organize over
$sortKey = 'id';
// Key to concatenate
$concatenateKey = 'kid';
// Separator string
$separator = ', ';
foreach($rows as $row) {
// Guard against invalid rows
if (!isset($row[$sortKey]) || !isset($row[$concatenateKey])) {
continue;
}
// Current identifier
$identifier = $row[$sortKey];
if (!isset($concatenated[$identifier])) {
// If no matching row has been found yet, create a new item in the
// concatenated output array
$concatenated[$identifier] = $row;
} else {
// An array has already been set, append the concatenate value
$concatenated[$identifier][$concatenateKey] .= $separator . $row[$concatenateKey];
}
}
// Do something useful with the output
var_dump($concatenated);

Answer 2

If you only have the data in a CSV file, I think that the easiest way to do what you want is build an associative array using the common data as key and modifing it if exists:
$array=[];
while ($a=fgetcsv($handle)){
if (isset($array[$a[0]."-".$a[1]."-".$a[2]])) {
$array[$a[0]."-".$a[1]."-".$a[2]].=",".$a[3];
}
else {
$array[$a[0]."-".$a[1]."-".$a[2]]=$a[3];
}
}