Question

Consider an object that is a list of arrays:

a=[array([1,2,3]),array(2,5,10,20)]

In its own funny way, this thing has two dimensions. The list itself is one dimension, and it contains objects which are 1D. Is there an easy way to distinguish between a above and a list like b=[1,3,6,9,11] which is simply 1D, and c=1, which is a 0D scalar? I want a function dimens() such that dimens(a) returns 2, dimens(b) returns 1, and dimens(c) returns 0.

I am doing it by testing the shape of the first element in the list, but I feel like there may be a cleaner approach.

Answer 1

def dimens(l):
    try:
        size = len(l)
    except TypeError: # not an iterable
        return 0
    else:
        if size: # non-empty iterable
            return 1 + max(map(dimens, l))
        else: # empty iterable
            return 1

print(dimens([[1,2,3],[2,5,10,[1,2]]]))
print(dimens(np.zeros([6,5,4,3,2,1])))

Output

3
6

Answer 2

Here's my function:

def dimens(x):
    s=shape(x)
    if len(s)==0:
        return 0 #the input was a scalar
    s2=shape(x[0])
    if len(s2)==0:
        return 1 #each element of the list was a scalar
    else:
        #each element of the list was a vector or array
        if len(s2)==1:
            if len(shape(s2[0]))==0:
                return 2 #the first element of the top list was a 1D vector and the first element of that vector was a scalar
        return 3 #there were more than 2 dimensions involved

Testing:

a=[array([1,2,3]),array([2,5,10,20])]
b=[1,3,6,9,11]
c=1
d=[[a]]+[[a]]

print dimens(a)
2
print dimens(b)
1
print dimens(c)
0
print dimens(d)
3

Limitations:

Only goes up to three dimensions (this is enough for my application)
Only tests the first element, so it assumes that each element has the same dimensionality (which is fine for my application since my 2D case will be a list of all arrays, not a list that has a mix of arrays and scalars)

Can anyone do better?

Answer 3

You can use isinstance method to distinguish between the two arrays

Lets consider the first list

a = [1,2,3]

Here the first element is an integer hence isinstance(a[0],int) will return true

For the second array b = [[1,2][3,4]] the first element is an array so isinstance(b[0],int) will return false. You can check the second list by using isinstance(b[0],list)

I am using list in place of array but it will work with arrays also

How to determine the dimensions of a mix of lists and arrays?

3 个答案: