Edwige Pezzulli - 1 month ago 21

Python Question

I have a matrix with

`N = 250000`

`M = 10`

I want to sort the matrix for decreasing values of the first column,

so I write:

`matrix=np.loadtxt("matrix.dat")`

np.sort(matrix)

matrix=matrix[::-1]

But the

`np.sort`

Anyone knows how to resolve this problem?

Thank you very much

Answer

This will sort a matrix for decreasing values of the first column

```
import numpy as np
# Generate a matrix of data
matrix = np.random.rand(5,4)
# Find the ordering of the first column (in increasing order)
ind = np.argsort(matrix[:,0])
# Switch the ordering (so it's decreasing order)
rind = ind[::-1]
# Return the matrix with rows in the specified order
matrix = matrix[rind]
```