function pluck( data, key ) {
	var out;
	var i;
	out = [];
	for ( i = 0; i < data.length; i++ ) {
		out.push( [ i, data[i][key] ] );
	}
	return out;
}
Extracts a list of property values. The list consists of two-element tuples where the first element is the element index and the second element is the extracted value.

@param {ObjectArray} data - input data
@param {string} key - key on which to select values
@returns {ArrayArray} array of tuples, where each tuple consists of the value index and the extracted value