CODEWITHSUNDEEP
pythonarraysnumpymesh
Basj
Basj

Reputation: 46371

Matrix in which rows are coordinates of points of a meshgrid

In this tutorial I find code like

import numpy as np
x = np.linspace(-5, 5, 20)
y = np.linspace(-1, 1, 10)
Y, X = np.meshgrid(y, x) 
xy = np.vstack([X.ravel(), Y.ravel()]).T
print(xy)

Isn't there a shorter way to get a matrix where rows are coordinates of points of the meshgrid, than using meshgrid+vstack+ravel+transpose?

Output:

[[-5.         -1.        ]
 [-5.         -0.77777778]
 [-5.         -0.55555556]
 [-5.         -0.33333333]
 [-5.         -0.11111111]
 [-5.          0.11111111]
 [-5.          0.33333333]
 [-5.          0.55555556]
 [-5.          0.77777778]
 [-5.          1.        ]
 [-4.47368421 -1.        ]
 [-4.47368421 -0.77777778]
 ...

Upvotes: 0

Views: 328

Answers (3)

Chris Flesher
Chris Flesher

Reputation: 1017

Here is a one-liner using meshgrid:

import numpy as np

x = np.linspace(-5, 5, 20)
y = np.linspace(-1, 1, 10)
xy = np.stack(np.meshgrid(x, y, indexing='ij'), -1).reshape(-1, 2)
print(xy)

Upvotes: 1

Ante
Ante

Reputation: 5448

Here is implementation with repeat and tile methods.

import numpy as np

x = np.linspace(-5, 5, 20)
y = np.linspace(-1, 1, 10)
xy = np.empty((len(x) * len(y), 2))
xy[:, 0] = np.repeat(x, len(y))
xy[:, 1] = np.tile(y, len(x))
print(xy)

I suppose meshgrid method uses same approach to fill it's result matrix.

Upvotes: 1

tel
tel

Reputation: 13999

You can skip meshgrid and get what you want more directly by just taking the cartesian product of x and y:

from itertools import product
import numpy as np

x = np.linspace(-5, 5, 20)
y = np.linspace(-1, 1, 10)
xy = np.array(list(product(x,y)))
print(xy)

Output:

[[-5.         -1.        ]
 [-5.         -0.77777778]
 [-5.         -0.55555556]
 [-5.         -0.33333333]
 [-5.         -0.11111111]
 [-5.          0.11111111]
 [-5.          0.33333333]
 [-5.          0.55555556]
 [-5.          0.77777778]
 [-5.          1.        ]
 [-4.47368421 -1.        ]
 [-4.47368421 -0.77777778]
 [-4.47368421 -0.55555556]
 [-4.47368421 -0.33333333]
...
]

Upvotes: 2

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