How to sort and array by indices sequence of another array-CodePudding

Given I have two arrays:

array1 = np.array([np.nan,np.nan,np.nan,np.nan,2,np.nan,1,np.nan,np.nan,5,np.nan,np.nan,6,np.nan,10,9,np.nan])
array2 = np.array([np.nan,np.nan,np.nan,np.nan,45,np.nan,33,np.nan,np.nan,32,np.nan,np.nan,44,np.nan,10,53,np.nan])

I want to get array2 sorted in ascending order of array1 elements with same nan sequence: [np.nan,np.nan,np.nan,np.nan,32,np.nan,10,np.nan,np.nan,33,np.nan,np.nan,44,np.nan,53,45,np.nan]

Seems I could use np.argsort(array1) = [ 6 4 9 12 15 14 0 13 11 10 8 5 3 2 1 7 16] if there's a command to move elements in array2 like : put an element with index "6" to the first not nan place etc

Any ideas?

CodePudding user response：

Remove NaN, sort, add NaN.

from operator import itemgetter

#remove NaN
a = [x for x in array1 if not np.isnan(x)]
b = [y for y in array2 if not np.isnan(y)]
# a == [2.0, 1.0, 5.0, 6.0, 10.0, 9.0]
# b == [45.0, 33.0, 32.0, 44.0, 10.0, 53.0]


# sort
c = map(itemgetter(1), sorted(zip(a, b)))
# list(c) == [33.0, 45.0, 32.0, 44.0, 53.0, 10.0]

# add NaN
d = [(np.nan if np.isnan(x) else next(c)) for x in array1]
# d == [nan, nan, nan, nan, 33.0, nan, 45.0, nan, nan, 32.0, nan, nan, 44.0, nan, 53.0, 10.0, nan]

Note that the suggestion in Akshay Sehgal's answer is likely faster than mine, since it uses numpy directly rather than python lists and iterators.

CodePudding user response：

You can do this with numpy by overwriting the view over the second array for non nan elements.

idx = array1[~np.isnan(array1)].argsort()

array2[~np.isnan(array2)] = array2[~np.isnan(array2)][idx]
array2

array([nan, nan, nan, nan, 33., nan, 45., nan, nan, 32., nan, nan, 44.,
       nan, 53., 10., nan])

Another "cleaner" way to do this is to just sort the arrays as is, remove nans and then overwrite the view for array2 as in the previous approach.

ordered = array2[array1.argsort()]
ordered = ordered[~np.isnan(ordered)]

array2[~np.isnan(array2)] = ordered
array2

array([nan, nan, nan, nan, 33., nan, 45., nan, nan, 32., nan, nan, 44.,
       nan, 53., 10., nan])