WordPress core contributors by version. Input data from https://api.wordpress.org/core/credits/1.1/?version=x.x

wp-core-contributors-by-version.php

<?php

$data_dir = 'c:/server/www/dev/data/';
$releases = [ ];

foreach ( range( 3.2, 4.0, 0.1 ) as $version ) {

	$version = number_format( $version, 1 );
	$data    = json_decode( file_get_contents( $data_dir . $version . '.json' ), true );
	$groups  = wp_list_pluck( $data['groups'], 'data' );
	unset( $groups['libraries'] );
	$groups               = array_map( 'array_keys', $groups );
	$releases[ $version ] = call_user_func_array( 'array_merge', $groups );
	$releases[ $version ] = array_map( 'strtolower', $releases[ $version ] );
	$releases[ $version ] = array_unique( $releases[ $version ] );
}

$all_contributors = $releases['3.2'];
unset( $releases['3.2'] );

$total_counts  = [ ];
$repeat_counts = [ ];
$new_counts    = [ ];

foreach ( $releases as $version => $contributors ) {
	$new_contributors = array_filter( $contributors, function ( $contributor ) use ( $all_contributors ) {
		return ! in_array( strtolower( $contributor ), $all_contributors );
	} );
	$all_contributors = array_unique( array_merge( $all_contributors, $contributors ) );
	$new_count        = count( $new_contributors );
	$total_count      = count( $contributors );
	$total_counts[]   = $total_count;
	$repeat_counts[]  = $total_count - $new_count;
	$new_counts[]     = $new_count;
}

?>

	<style type="text/css">
		#legend .bar-legend li {
			display:         inline;
			list-style-type: none;
			text-align:      center;
			margin-left:     10px;
		}

		#legend .bar-legend span {
			display:        inline-block;
			width:          16px;
			height:         16px;
			vertical-align: middle;
			margin:         0 5px;
		}
	</style>
	<div id="legend"></div>
	<canvas id="myChart" width="800" height="400"></canvas>
	<script type="text/javascript" src="//cdn.jsdelivr.net/chart.js/1.0.1-beta.4/Chart.min.js"></script>
	<script type="text/javascript">
		var ctx = document.getElementById("myChart").getContext("2d");
		var data = {
			labels  : <?= json_encode(array_keys($releases)) ?>,
			datasets: [
				{
					label    : "Total contributors",
					fillColor: "rgba(220,220,220,0.5)",
					data     : <?= json_encode($total_counts) ?>
				},
				{
					label    : "Repeat contributors",
					fillColor: "rgba(0, 168, 240,0.5)",
					data     : <?= json_encode($repeat_counts) ?>
				},
				{
					label    : "New contributors",
					fillColor: "rgba( 192, 216, 0,0.5)",
					data     : <?= json_encode($new_counts) ?>
				}
			]
		};
		var myBarChart = new Chart(ctx).Bar(data);
		var legendHolder = document.getElementById('legend');
		legendHolder.innerHTML = myBarChart.generateLegend();
	</script>
<?php