Extracting outermost size of an array?

[MoAly98]

Hi,
I ran into this issue when I simply wanted to check if an awkward array is empty or not after I filtered data from it. My array had a type that looks like:

N  * {"field1": X, "field2": var*Y}

which means that ak.size fails to compute the array size. I am wondering if there is a method to extract the value N from the array without turning it into a list of lists?

Thanks,
Mo

[agoose77]

ak.size is a function that implements np.size when the arrays are rectilinear. In your case, you do not have a rectilinear array, so this fails. The length N is just len(array). For more complex length calculations there are ak.count and ak.num, which return slightly different length information that you can use.

[jpivarski]

That's right, ak.count and ak.num are the counting functions. You likely want ak.num for any "how many XYZs do I have?" questions, since this function treats records ({"field1": X, "field2": var*Y} objects) as units, whereas ak.count is a reducer that cuts across objects, as described more fully in the ak.sum documentation.

Since your type is just

N  * {"field1": X, "field2": var*Y}

and I take it you want to know "N", just do len(array). It happens to be the case that ak.num with axis=0 is the same as len(array).

---

Also, if you made the array with cuts by

array = array_without_cuts[cuts]

then you can also do

np.count_nonzero(cuts)

to get the number of entries that would pass without even applying the cut.