参考链接： Python中的numpy.nanargmax
http://blog.csdn.net/pipisorry/article/details/51822775
numpy排序、搜索和计数函数和方法。（重新整合过的）
排序Sorting
sort(a[, axis, kind, order])
Return a sorted copy of an array.
lexsort(keys[, axis])
Perform an indirect sort using a sequence of keys.
argsort(a[, axis, kind, order])
Returns the indices that would sort an array.
