Martin wrote: > On Jul 27, 1:46 pm, Peter Otten <__pete...@web.de> wrote: >> Martin wrote: >> > On Jul 27, 12:42 pm, Peter Otten <__pete...@web.de> wrote: >> >> Martin wrote: >> >> > I am new to python and I was wondering if there was a way to speed >> >> > up the way I index 2D arrays when I need to check two arrays >> >> > simultaneously? My current implementations is (using numpy) >> >> > something like the following... >> >> >> > for i in range(numrows): >> >> > for j in range(numcols): >> >> >> > if array_1[i, j] == some_value or array_2[i, j] >= >> >> > array_1[i, >> >> > j] * some_other_value >> >> > array_1[i, j] = some_new_value >> >> >> array_1[(array_1 == some_value) | (array_2 >= array_1 * >> >> some_other_value)] = some_new_value >> >> >> maybe? >> >> > So I tried... >> >> > band_1[(array_1 == 255) or (array_2 >= array_1 * factor)] = 0 >> >> > which led to >> >> > ValueError: The truth value of an array with more than one element is >> > ambiguous. Use a.any() or a.all() >> >> > so not sure that works? >> >> Copy and paste -- or replace "or" with "|". > > apologies - I mistook that for a type for "or" > > I now get the following error... > > ValueError: shape mismatch: objects cannot be broadcast to a single > shape
It seems array_1 and array_2 have a -- dada! -- different shape. Assuming array_1 is the smaller one: numrows, numcols = array_1.shape array_1[(array_1 == some_value) | (array_2[:numrows,:numcols] >= array_1 * some_other_value)] = some_new_value There may be other options, but I'm not a numpy expert. Peter -- http://mail.python.org/mailman/listinfo/python-list
