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View Full Version : Python question - how to check the sign in an array

thomnor
February 3rd, 2008, 09:14 PM
Hi,

I wonder if it is possible to test if the next object in an array has changed its sign (from positive to negative, or vice versa) from the first element in the array.

Here's some pseudo code:

for i in range(n):
if some_array[i] has the opposite sign of some_array[0]:
some_array[i] = 0

I'm not a very experienced programmer, so there might be an easy solution I haven't thought of.

LaRoza
February 3rd, 2008, 09:20 PM
You used the same name in your code, so it is hard to tell your logic.

i = 0
for this_array in some_array:
if (this_array < 0 and some_array[i] > = 0) or (this_array >= 0 and some_array[i] < 0):
print "Signs opposite on element: %d" % i
else:
print "Signs aren't opposite"
i += 1

Jessehk
February 3rd, 2008, 09:46 PM
Something like this?

def sign(n):
if n > 0:
return 1
elif n == 0:
return 0
else:
return -1

def is_different_sign(arr, index):
return sign(arr[0]) != sign(arr[index])

numbs = [3, -2, 1, 4, -5]

for i in xrange(len(numbs)):
if is_different_sign(numbs, i):
numbs[i] = 0

print numbs

\$ python example.py
[3, 0, 1, 4, 0]

thomnor
February 3rd, 2008, 10:18 PM