On 09/21/2012 11:25 AM, Steven D'Aprano wrote: > On 22/09/12 01:07, Bala subramanian wrote: >> Friends, >> May i know why do get a Valuerror if i check any value in a is between >> 3.0 to 5.0 ?
To summarize, with a numpy array called a, the OP is getting an error doing: (3 < a < 5).any() > This tries to calculate: > > (3 < a) and (a < 5) > > py> 3 < a > array([False, False, False, True, True, True], dtype=bool) > py> a < 5 > array([ True, True, True, True, True, False], dtype=bool) > > but combining them with the "and" operator is ambiguous: > > py> (3 < a) and (a < 5) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > ValueError: The truth value of an array with more than one element > is ambiguous. Use a.any() or a.all() > > Since the boolean "and" of the two arrays never gets calculated, > the any method never gets called. You could do: > > > py> (3 < a).any() and (a < 5).any() > True > > which I think does what you want. > I think not. The last expression you give will even return true if one of the values is > 3 and a DIFFERENT value is < 5. And i suspect the OP only wants a TRUE if at least one item in the array is between 3 and 5. I know nothing about numpy, but does it have a way to do an element-wise AND of two bool arrays of the same size? Maybe it's a function call and not 'and' Or maybe it's the & operator or something. I find the operator overloading i've seen in numpy to be very confusing, so I haven't tried to download it and try it out. Maybe if I read the docs directly, instead of just seeing examples and problems here, I'd think differently. -- DaveA _______________________________________________ Tutor maillist - Tutor@python.org To unsubscribe or change subscription options: http://mail.python.org/mailman/listinfo/tutor
