CODEWITHSUNDEEP
pythonarraysnumpyif-statementequality
auden
auden

Reputation: 1157

Checking that all items in a list (numpy arrays) are equal

I have a function in my program that needs to check and make sure that all items in a list (which are all numpy arrays) are equal. The if statement that does this starts with

if np.array_equal(qstatnum[gatnum].count(qstatnum[gatnum][0]), len(qstatnum[gatnum])) == True:

This line gives the error

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

I am unsure what the problem is. Any help would be appreciated. Thanks!

Edit: Per request, full if-else statement in code

if np.array_equal(qstatnum[gatnum].count(qstatnum[gatnum][0]), len(qstatnum[gatnum])) == True:
    if np.array_equal(qstatnum[gatnum][0], [0,1]) == True:
        return qstat
    elif np.array_equal(qstatnum[gatnum][0], [1,0]) == True:
        return singates[typegat2](qstat)
    else:
        print("superposition not yet implemented")
else:
    return qstat

Apologies for not including, was trying to make the problem as small as possible.

Upvotes: 1

Views: 838

Answers (3)

Praveen
Praveen

Reputation: 7222

You don't seem to be using array_equal correctly. The inputs to array_equal must be arrays, whereas you seem to be passing len of something, which is a number...

If l1 and l2 are your two lists of arrays, you're probably looking for something like:

if all(np.array_equal(i, j) for i, j in zip(l1, l2)):
    # Do something

For example,

>>> l1 = [np.arange(3), np.arange(5)]
>>> l2 = [np.r_[0:3], np.r_[0:5]]
>>> if all(np.array_equal(i, j) for i, j in zip(l1, l2)):
...     print('yes')
...     
yes

Edit

If you're trying to show that all arrays in your list are equal to each other, then you can just show that all of them are equal to the first:

l = [np.arange(3), np.arange(3), np.arange(3)]
if all(np.array_equal(i, l[0]) for i in l[1:]):
    print('All equal!')

Upvotes: 2

Wasi Ahmad
Wasi Ahmad

Reputation: 37691

As @Praveen already mentioned, it looks like you want to compare two numbers only! If that is the case, then you don't need to use numpy.array_equal().

Since, you didn't provide your code, I am unable to explain why you are getting this error. But I am sharing a simple here to let you know what the error means.

Example:

x = np.arange(0, 2, 0.5)
print(x) # [ 0.   0.5  1.   1.5]
y = 2*x
print(y) # [ 0.  1.  2.  3.]

if y <= 1.0:
    print ("ok")

This program gives the following error.

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all()

If you print the value of the boolean expression:

print(y<=1.0)

It prints-

[True True False False]

So, updating the if condition as follows make the program work.

if np.all(y <= 1.0):
    print ("ok")

So, I guess, you can do something like this to solve your problem as well.

if np.all(np.array_equal(qstatnum[gatnum].count(qstatnum[gatnum][0]), len(qstatnum[gatnum]))) == True:

Upvotes: 1

reidjs
reidjs

Reputation: 169

I do not have numpy unfortunately, but here is how I would check if all items in a list were equal. 

for i in range(len(arr)):
for j in range(i+1, len(arr)):
    if arr[i] != arr[j]:
        print ("items are not all equal");

Hope that helps.

Upvotes: 0

Related Questions