CODEWITHSUNDEEP
python-3.xnumpy
Vlad Crow
Vlad Crow

Reputation: 39

Change int array into string array based on its values

I have a nparray that contains 0 and 1 values 

k = np.array([0, 1, 1, 0 ,1])

I want to transform the array into an array that contains 'blue' if the value is 0 and 'red' if the value is 1. I prefer to know the fastest way possible

Upvotes: 2

Views: 51

Answers (1)

Divakar
Divakar

Reputation: 221574

You can use np.take to index into a an array/list of 2 elements with those k values as indices, like so -

np.take(['blue','red'],k)

Sample run -

In [19]: k = np.array([0, 1, 1, 0 ,1])

In [20]: np.take(['blue','red'],k)
Out[20]: 
array(['blue', 'red', 'red', 'blue', 'red'], 
      dtype='|S4')

With the explicit indexing method -

In [23]: arr = np.array(['blue','red'])

In [24]: arr[k]
Out[24]: 
array(['blue', 'red', 'red', 'blue', 'red'], 
      dtype='|S4')

Or with initialization with one string and then assigning the other one -

In [41]: out = np.full(k.size, 'blue')

In [42]: out[k==1] = 'red'

In [43]: out
Out[43]: 
array(['blue', 'red', 'red', 'blue', 'red'], 
      dtype='|S4')

Runtime test

Approaches -

def app1(k):
    return np.take(['blue','red'],k)

def app2(k):
    arr = np.array(['blue','red'])
    return arr[k]

def app3(k):
    out = np.full(k.size, 'blue')
    out[k==1] = 'red'
    return out

Timings -

In [46]: k = np.random.randint(0,2,(100000))

In [47]: %timeit app1(k)
    ...: %timeit app2(k)
    ...: %timeit app3(k)
    ...: 
1000 loops, best of 3: 413 µs per loop
10000 loops, best of 3: 103 µs per loop
1000 loops, best of 3: 908 µs per loop

Upvotes: 3

Related Questions