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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/ml-features.md | 22 |
1 files changed, 20 insertions, 2 deletions
diff --git a/docs/ml-features.md b/docs/ml-features.md index 57605bafbf..dad1c6db18 100644 --- a/docs/ml-features.md +++ b/docs/ml-features.md @@ -503,6 +503,7 @@ for more details on the API. `StringIndexer` encodes a string column of labels to a column of label indices. The indices are in `[0, numLabels)`, ordered by label frequencies, so the most frequent label gets index `0`. +The unseen labels will be put at index numLabels if user chooses to keep them. If the input column is numeric, we cast it to string and index the string values. When downstream pipeline components such as `Estimator` or `Transformer` make use of this string-indexed label, you must set the input @@ -542,12 +543,13 @@ column, we should get the following: "a" gets index `0` because it is the most frequent, followed by "c" with index `1` and "b" with index `2`. -Additionally, there are two strategies regarding how `StringIndexer` will handle +Additionally, there are three strategies regarding how `StringIndexer` will handle unseen labels when you have fit a `StringIndexer` on one dataset and then use it to transform another: - throw an exception (which is the default) - skip the row containing the unseen label entirely +- put unseen labels in a special additional bucket, at index numLabels **Examples** @@ -561,6 +563,7 @@ Let's go back to our previous example but this time reuse our previously defined 1 | b 2 | c 3 | d + 4 | e ~~~~ If you've not set how `StringIndexer` handles unseen labels or set it to @@ -576,7 +579,22 @@ will be generated: 2 | c | 1.0 ~~~~ -Notice that the row containing "d" does not appear. +Notice that the rows containing "d" or "e" do not appear. + +If you call `setHandleInvalid("keep")`, the following dataset +will be generated: + +~~~~ + id | category | categoryIndex +----|----------|--------------- + 0 | a | 0.0 + 1 | b | 2.0 + 2 | c | 1.0 + 3 | d | 3.0 + 4 | e | 3.0 +~~~~ + +Notice that the rows containing "d" or "e" are mapped to index "3.0" <div class="codetabs"> |