diff options
Diffstat (limited to 'doc')
| -rw-r--r-- | doc/neps/missing-data.rst | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/doc/neps/missing-data.rst b/doc/neps/missing-data.rst index de00cbb74..265b6304f 100644 --- a/doc/neps/missing-data.rst +++ b/doc/neps/missing-data.rst @@ -677,7 +677,7 @@ This gives us the following additions to the PyArrayObject:: * NPY_ARRAY_OWNNAMASK enabled, it owns this memory and * must call PyArray_free on it when destroyed. */ - char *maskdata; + npy_uint8 *maskdata; /* * Just like dimensions and strides point into the same memory * buffer, we now just make the buffer 3x the nd instead of 2x @@ -708,6 +708,19 @@ PyArray_ContainsNA(PyArrayObject* obj) true if the array has NA support AND there is an NA anywhere in the array. +The format of the mask itself is designed to indicate whether an +element is masked or not, as well as contain a payload so that multiple +different NAs with different payloads can be used in the future. +Initially, we will simply use the payload 0. + +In order to allow the combination of masks to be a simple 'min' operation, +we make the dtype be npy_uint8, and use bit 7 to indicate whether +the value with mask 'm' is masked ((m&0x80) == 0) or unmasked +((m&0x80) == 0x80). The rest of the bits are the payload, which +is (m&0x7f). A consequence of this is that payloads with smaller values +are propagated. This design gives 128 payload values to masked elements, +and 128 payload values to unmasked elements. + ******************************************** C Iterator API Changes: Iteration With Masks ******************************************** @@ -755,12 +768,13 @@ NPY_ITER_ARRAYMASK into the NA bitpattern when copying from the buffer to the array. -NPY_ITER_VIRTUALMASK - Indicates that the mask is not an array, but rather created on - the fly by the inner iteration code. This allocates enough buffer - space for the code to write the mask into, but does not have - an actual array backing the data. There can only be one such - mask, and there cannot also be an array mask. +NPY_ITER_VIRTUAL + Indicates that this operand is not an array, but rather created on + the fly for the inner iteration code. This allocates enough buffer + space for the code to read/write data, but does not have + an actual array backing the data. When combined with NPY_ITER_ARRAYMASK, + allows for creating a "virtual mask", specifying which values + are unmasked without ever creating a full mask array. Iterator NA-array Features ========================== |