diff options
Diffstat (limited to 'doc/neps')
| -rw-r--r-- | doc/neps/c-masked-array.rst | 43 |
1 files changed, 37 insertions, 6 deletions
diff --git a/doc/neps/c-masked-array.rst b/doc/neps/c-masked-array.rst index 68149d004..acf7ec6d1 100644 --- a/doc/neps/c-masked-array.rst +++ b/doc/neps/c-masked-array.rst @@ -157,6 +157,35 @@ an np.array *a* are:: Exactly like a.copy(), except always produces an array without a mask and uses 'fillvalue' for any masked values. +Masked Element-wise UFuncs +========================== + +As part of the implementation, ufuncs and other operations will +have to be extended to support masked computation. Because this +is a useful feature in general, even outside the context of +a masked array, in addition to working with masked arrays ufuncs +will take an optional 'mask=' parameter which allows the use +of boolean arrays to choose where a computation should be done. This +functions similar to a "where" clause on the ufunc.:: + + np.add(a, b, out=b, mask=(a > threshold)) + +If the 'out' parameter isn't specified, use of the 'mask=' parameter +will produce a array with a mask as the result. A benefit of this +operation is that it provides a way to temporarily treat an object +with a mask, without making it a masked array which adds the mask +permanently. + +Reduction operations like 'sum', 'prod', 'min', and 'max' will operate as +if the values weren't there, applying the operation to the unmasked +values. If all the input values are masked, 'sum' and 'prod' will produce +the additive and multiplicative identities respectively, while 'min' +and 'max' will produce masked values. + +Statistics operations which require a count, like 'mean' and 'std' will +also use the unmasked value counts for their calculations, and produce +masked values when all the inputs are masked. + Unresolved Design Questions =========================== @@ -168,10 +197,12 @@ while the later preserves type information, so the correct choice will require some discussion to resolve. The existing masked array implementation has a "hardmask" feature, -which freezes the mask. Boolean indexing could for instance return -a hardmasked array instead of a flattened array with the arbitrary -choice of C-ordering as it currently is. This could be an internal -array flag, with a.mask.harden() and a.mask.soften() performing the -functions of a.harden_mask() and a.soften_mask() in the current masked -array. There would also be an a.mask.ishard property. +which freezes the mask. This would be an internal +array flag, with 'a.mask.harden()' and 'a.mask.soften()' performing the +functions of 'a.harden_mask()' and 'a.soften_mask()' in the current masked +array. There would also need to be an 'a.mask.ishard' property. + +If the hardmask feature is implemented, boolean indexing could +return a hardmasked array instead of a flattened array with the +arbitrary choice of C-ordering as it currently does. |