fix: teach column and getitem to respect validity#1927
Closed
danking wants to merge 8 commits into
Closed
Conversation
Mask sets entries of an array to null. I like the analogy to light: the array is a sequence of lights (each value might be a different wavelength). Null is represented by the absence of light. Placing a mask (i.e. a piece of plastic with slits) over the array causes those values where the mask is present (i.e. "on", "true") to be dark. An example in pseudo-code: ```rust a = [1, 2, 3, 4, 5] a_mask = [t, f, f, t, f] mask(a, a_mask) == [null, 2, 3, null, 5] ``` Specializations --------------- I only fallback to Arrow for two of the core arrays: - Sparse. I was skeptical that I could do better than decompressing and applying it. - Constant. If the mask is sparse, SparseArray might be a good choice. I didn't investigate. For the non-core arrays, I'm missing the following. I'm not clear that I can beat decompression for run end. The others are easy enough but some amount of typing and testing. - fastlanes - fsst - roaring - runend - runend-bool - zigzag Naming ------ Pandas also calls this operation [`mask`](https://pandas.pydata.org/docs/reference/api/pandas.DataFrame.mask.html) but accepts an optional second argument which is an array of values to use instead of null (which makes Pandas' mask more like an `if_else`). Arrow-rs calls this [`nullif`](https://arrow.apache.org/rust/arrow/compute/fn.nullif.html). Arrow-cpp has [`if_else(condition, consequent, alternate)`](https://arrow.apache.org/docs/cpp/compute.html#cpp-compute-scalar-selections) and [`replace_with_mask(array, mask, replacements)`](https://arrow.apache.org/docs/cpp/compute.html#replace-functions) both of which can implement our `mask` by passing a `NullArray` as the third argument.
Contributor
Author
|
Will reopen after #1900 merges. |
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
No description provided.