On Thu, Sep 1, 2016 at 3:49 PM, Florian Lindner mailinglists@xgm.de wrote:

Hello,

thanks for your reply which was really helpful!

My problem is that I discovered that the data I got is rather unordered.

The documentation for reshape says: Read the elements of a using this

index order, and place the elements into the

reshaped array using this index order. ‘C’ means to read / write the

elements using C-like index order, with the last

axis index changing fastest, back to the first axis index changing

slowest. ‘F’ means to read / write the elements using

Fortran-like index order, with the first index changing fastest, and the

last index changing slowest.

With my data both dimensions change, so there is no specific ordering of

the points, just a bunch of arbitrarily mixed

"x y z value" data.

My idea is:

out = np.loadtxt(...) x = np.unique(out[:,0]) y = np.unique[out]:,1]) xx, yy = np.meshgrid(x, y)

values = lookup(xx, yy, out)

lookup is ufunc (I hope that term is correct here) that looks up the

value of every x and y in out, like

x_filtered = out[ out[:,0] == x, :] y_filtered = out[ out[:,1] == y, :] return y_filtered[2]

(untested, just a sketch)

Would this work? Any better way?

If the (x, y) values are actually drawn from a rectilinear grid, then you can use np.lexsort() to sort the rows before reshaping.

[~/scratch] |4> !cat random-mesh.txt 0.3 0.3 21 0 0 10 0 0.3 11 0.3 0.6 22 0 0.6 12 0.6 0.3 31 0.3 0 20 0.6 0.6 32 0.6 0 30

[~/scratch] |5> scrambled_nodes = np.loadtxt('random-mesh.txt')

# Note! Put the "faster" column before the "slower" column! [~/scratch] |6> i = np.lexsort([scrambled_nodes[:, 1], scrambled_nodes[:, 0]])

[~/scratch] |7> sorted_nodes = scrambled_nodes[i]

[~/scratch] |8> sorted_nodes array([[ 0. , 0. , 10. ], [ 0. , 0.3, 11. ], [ 0. , 0.6, 12. ], [ 0.3, 0. , 20. ], [ 0.3, 0.3, 21. ], [ 0.3, 0.6, 22. ], [ 0.6, 0. , 30. ], [ 0.6, 0.3, 31. ], [ 0.6, 0.6, 32. ]])

Then carry on with the reshape()ing as before. If the grid points that "ought to be the same" are not actually identical, then you may end up with some problems, e.g. if you had "0.300000000001 0.0 20.0" as a row, but all of the other "x=0.3" rows had "0.3", then that row would get sorted out of order. You would have to clean up the grid coordinates a bit first.

-- Robert Kern