function iqr( data, j ) {
	// Copy and sort data --> build X
	var arr;
	var i;
	arr = new Array( data.shape[0] );
	for ( i = 0; i < data.shape[0]; i++ ) {
		arr[ i ] = data.get( i, j );
	}
	arr.sort( ascending );
	return quantile( arr, 0.75 ) - quantile( arr, 0.25 );
}
Computes the inter-quartile range for a numeric array.

@private
@param {NumericArray} data - ndarray like data
@param {number} j - column index for which to get the IQR
@returns {number} inter-quartile range