[EMAIL PROTECTED] wrote: > I have two one-dimensional Numeric arrays, and I need to know the > indices in the second array of elements from the first. > > so if i had: > > a=array([2,4,6]) > b=array([2,3,4,5,6]) > > i want a function match that does this: > > >>>>match(a,b) > > array([0,2,4]) > > i have something that works, but it involves converting things to lists > and using 'in', and it is rather slow. if someone could point me to a > better solution, i would appreciate it.
If b is sorted, then you can use Numeric.searchsorted(b, a). Otherwise: In [28]: import Numeric as N In [29]: a = N.array([2,4,6]) In [30]: b = N.array([2,3,4,5,6]) In [31]: match = N.equal.outer(a, b) In [32]: idx = N.compress(N.sum(match), N.arange(len(b))) In [33]: idx Out[33]: array([0, 2, 4]) -- Robert Kern [EMAIL PROTECTED] "In the fields of hell where the grass grows high Are the graves of dreams allowed to die." -- Richard Harter -- http://mail.python.org/mailman/listinfo/python-list
