CODEWITHSUNDEEP
pythonarraysnumpydictionary
Python Learner
Python Learner

Reputation: 437

Retrieve python dictionary value by using numpy array as a key in time efficient way

I'm using python 3.6 .I have a numpy array let's say a.It's in this format

array(['0', '1', '2', ..., '3304686', '3304687', '3304688'],
      dtype='<U7')

I have another dictionary b={1: '012', 2: '023', 3: '045',.....3304688:'01288'}

I want to retrieve each value of b and store it in another numpy array by providing the value of a as a key to b. I was planning to try in this way

    z_array = np.array([])  

    for i in range(a.shape[0]):
        z=b[i]        
        z_array=np.append(z_array,z)

But looking the shape of a,I'm feeling that it will be very much time consuming. Can you please suggest me some alternate approach which will be time efficient?

Upvotes: 0

Views: 670

Answers (1)

Paul Panzer
Paul Panzer

Reputation: 53089

You could use np.frompyfunc, note that this will create an object array.

b = {str(i): i**3 for i in range(10**7)}
a = [str(i) for i in range(10**7)]
c = np.frompyfunc(b.__getitem__, 1, 1)(a)

or

c = np.frompyfunc(b.get, 1, 1)(a)

to indicate missing keys by None.

In the example with 10,000,000 items and as many lookups takes just a second or two. (Creating a and b takes longer)

Upvotes: 1

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