How to arrange a numpy list in order according to the order of a list or string-CodePudding

i have a numpy array:

import numpy as np
phrase = np.array(list("eholl")) 
a = 'hello'

i would like to sort the variable, according to the order of letters (h first, e second...) inside the variable "a" that result into the array ordered:

Tried:

z = np.sort(phrase, order=a)

print(z)

Output that i want:

hello

Error:

ValueError                                Traceback (most recent call last)
<ipython-input-10-64807c091753> in <module>
      2 phrase = np.array(list("eholl"))
      3 a = 'hello'
----> 4 z = np.sort(phrase, order=a)
      5 
      6 print(z)

<__array_function__ internals> in sort(*args, **kwargs)

/usr/local/lib/python3.7/dist-packages/numpy/core/fromnumeric.py in sort(a, axis, kind, order)
    996     else:
    997         a = asanyarray(a).copy(order="K")
--> 998     a.sort(axis=axis, kind=kind, order=order)
    999     return a
   1000 

**ValueError: Cannot specify order when the array has no fields.**

CodePudding user response：

order argument of np.sort is to specify which fields to compare first, second, etc. It doesn't help you.

If you don't require the immediate output of the sorting function is a numpy array, you can simply use built-in function sorted. You can specify a key function via its key argument. In your case, the sorting keys are the indices in a string, which can be obtained via str.find.

import numpy as np
phrase = np.array(list("eholl"))
refer_phrase = 'hello'

# sort by the first position of x in refer_phrase
sorted_phrase_lst = sorted(phrase, key=lambda x: refer_phrase.find(x))
print(sorted_phrase_lst)
# ['h', 'e', 'l', 'l', 'o']
sorted_phrase_str = ''.join(sorted_phrase_lst)
print(sorted_phrase_str)
# hello