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I am trying to delete every 8th column in a 1024x1024 matrix using this method but it takes a lot of time and it will be more difficult when I have to process millions of matrices. Could you please show me how can I delete every nth row or column starting from a certain row or column and using numpy, scipy or any other Python package?
Many thanks
521
Using the NumPy function np. delete() , you can delete any row and column from the NumPy array ndarray . Specify the axis (dimension) and position (row number, column number, etc.). It is also possible to select multiple rows and columns using a slice or a list.
To remove every nth element of a list in Python, utilize the Python del keyword to delete elements from the list and slicing. For your slice, you want to pass n for the slice step size.
It returns an array by deleting the elements at given index or indices. Now to remove multiple columns in the array we need to pass the given array and the 'array of index' of the columns to be deleted and axis=1 to the delete() method. Slice() method is used to pass a slice of column indices to the delete() method.
You can use np.delete giving the indices corresponding to every 8th row index. Let a be a 2D array or a matrix:
np.delete(a, list(range(0, a.shape[0], 8)), axis=0)
note the use of axis=0 indicating to operate along the rows. To operate along the columns:
np.delete(a, list(range(0, a.shape[1], 8)), axis=1)
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