Filter a 2D numpy array from an array of values

Question

Let's say I have a numpy array with the following shape :

nonSortedNonFiltered=np.array([[9,8,5,4,6,7,1,2,3],[1,3,2,6,4,5,7,9,8]])

I want to :

- Sort the array according to nonSortedNonFiltered[1] - Filter the array according to nonSortedNonFiltered[0] and an array of values

I currently do the sorting with :

sortedNonFiltered=nonSortedNonFiltered[:,nonSortedNonFiltered[1].argsort()]

Which gives : np.array([[9 5 8 6 7 4 1 3 2],[1 2 3 4 5 6 7 8 9]])

Now I want to filter sortedNonFiltered from an array of values, for example :

sortedNonFiltered=np.array([[9 5 8 6 7 4 1 3 2],[1 2 3 4 5 6 7 8 9]])
listOfValues=np.array([8 6 5 2 1])
...Something here...

> np.array([5 8 6 1 2],[2 3 4 7 9]) #What I want to get in the end

Note : Each value in a column of my 2D array is exclusive.

Divakar · Accepted Answer · 2015-08-04 12:47:10Z

2

You can use np.in1d to get a boolean mask and use it to filter columns in the sorted array, something like this -

output = sortedNonFiltered[:,np.in1d(sortedNonFiltered[0],listOfValues)]

Sample run -

In [76]: nonSortedNonFiltered
Out[76]: 
array([[9, 8, 5, 4, 6, 7, 1, 2, 3],
       [1, 3, 2, 6, 4, 5, 7, 9, 8]])

In [77]: sortedNonFiltered
Out[77]: 
array([[9, 5, 8, 6, 7, 4, 1, 3, 2],
       [1, 2, 3, 4, 5, 6, 7, 8, 9]])
In [78]: listOfValues
Out[78]: array([8, 6, 5, 2, 1])

In [79]: sortedNonFiltered[:,np.in1d(sortedNonFiltered[0],listOfValues)]
Out[79]: 
array([[5, 8, 6, 1, 2],
       [2, 3, 4, 7, 9]])

edited Aug 4, 2015 at 12:47

answered Aug 4, 2015 at 12:41

Divakar

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2 Comments

Olivier Giniaux Over a year ago

wow that's perfect ! I was implementing a loop but it was way too slow for my huge number of values. This works way better

Divakar Over a year ago

@OdgyGsf Yes, np.in1d is quite efficient to solve cases like this.

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