Eliminate empty values in python dict made of lists and arrays

Question

I want to eliminate all empty value from a dict whose values are a mix of lists and nd array. So I tried with:

    res = [ele for ele in ({key: val for key, val in sub.items() if val} for sub in test_list) if ele]

but I get the error

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

AttributeError: 'list' object has no attribute 'any'

I get the error

AttributeError: 'list' object has no attribute 'any'

So I am wondering if there is a more general way to delete empty values in python dict.

Please fix the post to show the code that uses any; you copy-pasted the error message a second time instead. — Karl Knechtel
– Karl Knechtel, Commented Feb 3, 2021 at 15:23
But more importantly: where you wrote {key: val for key, val in sub.items() if val}, what is the actual rule that you have in mind with if val? With plain lists, an empty list will fail this and every other possible list will pass; is that what you intend? With the Numpy arrays, which should pass and which should fail? — Karl Knechtel
– Karl Knechtel, Commented Feb 3, 2021 at 15:25
You're calling array.any() when you should be doing any(array), which is why you're getting the second error. any is a built in function and not an attribute of a generic python array. (Fixing this is probably not going to fix your function but it is the cause of the error) — ICW
– ICW, Commented Feb 3, 2021 at 16:20

Jacob Faib · Accepted Answer · 2021-02-03 15:31:42Z

1

A common way to check empty for empty lists is to check len(list). So assuming your dict() looks like so

myDict = {
  1: [1,2,3],
  2: [],
  3: np.array([[1,2],[3,4],[5,6]])
}

Your list comprehension might look like

res = {k:v for k,v in myDict.items() if len(v)}

Note the len(v) in the dict comprehension

edited Feb 3, 2021 at 15:31

answered Feb 3, 2021 at 15:23

Jacob Faib

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soundstripe · Accepted Answer · 2021-02-03 15:32:45Z

1

I think you've made this one more step complicated than necessary (as well as not including a complete example!)

The following example creates a new dict res with all values of test_dict that have non-empty values. I used len() here because that works on both lists and nd-arrays. For just lists, I'd omit the call to len() and just use val.

test_dict = {1: [], 2: [1,2,3], 3: [4,5,6]}
res = {key: val for key, val in test_list.items() if len(val)}

If you are wanting to use any(), you'd be finding dict values that are lists that contain at least one truthy item:

test_dict = {1: [], 2: [1,2,3], 3: [4,5,6]}
res = {key: val for key, val in test_list.items() if any(val)}

answered Feb 3, 2021 at 15:32

soundstripe

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Red · Accepted Answer · 2021-02-03 16:07:22Z

0

@Jacob's answer works fine, though it is really inefficient.

Instead, you can take advantage of the built-in filter() method to filter out the empty dictionaries, and use the dict() method instead of using a dict comprehension:

res = filter(None, (dict(i for i in sub.items() if len(i[1])) for sub in test_list))

answered Feb 3, 2021 at 16:07

Red

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