PERF: Use iloc instead of values, which is slower on pandas 0.17
PERF: Use iloc instead of values, which is slower on pandas 0.17

umuzungu/zipline,bartosh/zipline,florentchandelier/zipline,Scapogo/zipline,bartosh/zipline,wilsonkichoi/zipline,enigmampc/catalyst,alphaBenj/zipline,magne-max/zipline-ja,magne-max/zipline-ja,quantopian/zipline,umuzungu/zipline,nborggren/zipline,Scapogo/zipline,enigmampc/catalyst,florentchandelier/zipline,humdings/zipline,humdings/zipline,alphaBenj/zipline,nborggren/zipline,wilsonkichoi/zipline,quantopian/zipline