[Numpy-discussion] Fancy Indexing of Structured Arrays is Slow
dave.hirschfeld at gmail.com
Thu May 15 08:31:50 EDT 2014
As can be seen from the code below (or in the notebook linked beneath) fancy
indexing of a structured array is twice as slow as indexing both fields
independently - making it 4x slower?
I found that fancy indexing was a bottleneck in my application so I was
hoping to reduce the overhead by combining the arrays into a structured
array and only doing one indexing operation. Unfortunately that doubled the
time that it took!
Is there any reason for this? If not, I'm happy to open an enhancement issue
on GitHub - just let me know.
In : nrows, ncols = 365, 10000
In : items = np.rec.fromarrays(randn(2,nrows, ncols), names=
In : row_idx = randint(0, nrows, ncols)
...: col_idx = np.arange(ncols)
In : %timeit filtered_items = items[row_idx, col_idx]
100 loops, best of 3: 3.45 ms per loop
In : %%timeit
...: widgets = items['widgets'][row_idx, col_idx]
...: gadgets = items['gadgets'][row_idx, col_idx]
1000 loops, best of 3: 1.57 ms per loop
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