How to create a numpy array from 2 lists

Question

I have a count of integer frequencies that I am trying to get into an array. L1 are the integers from 1 to 9, but only if they occur, I want to use this as the array index. L2 is the frequency of the integer and I want that to be entered in the array.

L1 = [1,3,4,5,6,7,8,9] #no twos occurred in the data so 2 is not in L1

L2 = [6,7,1,2,8,4,2,1]

The out put I want to get is: A1 = [[6,0,7],[1,2,8],[4,2,1]] I feel like I'm missing something but this is my last attempt:

for num in L1 and count in L2:
    a1[:num] = L2[:count]

hpaulj · Accepted Answer · 2021-09-30 22:38:53Z

1

Make the list arrays for ease of use:

In [286]: L1 = np.array([1,3,4,5,6,7,8,9])
     ...: L2 = np.array([6,7,1,2,8,4,2,1])

Make a place to put values:

In [287]: res = np.zeros(10,int)
In [288]: res[L1]
Out[288]: array([0, 0, 0, 0, 0, 0, 0, 0])
In [289]: res[L1]=L2
In [290]: res
Out[290]: array([0, 6, 0, 7, 1, 2, 8, 4, 2, 1])

oops, offset a bit.

In [291]: res = np.zeros(10,int)
In [292]: res[L1-1]=L2
In [293]: res
Out[293]: array([6, 0, 7, 1, 2, 8, 4, 2, 1, 0])

correct the initial size, and reshape:

In [294]: res = np.zeros(9,int)
In [295]: res[L1-1]=L2
In [296]: res.reshape(3,3)
Out[296]: 
array([[6, 0, 7],
       [1, 2, 8],
       [4, 2, 1]])

answered Sep 30, 2021 at 22:38

hpaulj

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1 Comment

Mercredi Over a year ago

Awesome! thank you!

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