lib/vega.js
function sources(k) {
      (src[k] || []).forEach(function(s) { deps[s] = k; sources(s); });
    }
function sources(k) {
      (src[k] || []).forEach(function(s) { deps[s] = k; sources(s); });
    }
function sources ( k ) { ( src [ k ] || [ ] ) . forEach ( function ( s ) { deps [ s ] = k ; sources ( s ) ; } ) ; }
collect source data set dependencies
collect source data set dependencies