Github user feynmanliang commented on a diff in the pull request:
https://github.com/apache/spark/pull/8267#discussion_r37346802
--- Diff: docs/ml-features.md ---
@@ -1389,3 +1389,145 @@ print(output.select("features", "clicked").first())
# Feature Selectors
+## VectorSlicer
+
+`VectorSlicer` is a transformer that takes a feature vector and outputs a
new feature vector with a sub-array of the original features. It is useful for
extracting features from a vector column.
+
+`VectorSlicer` accepts a vector column with a specified indices, then
outputs a new vector column whose values are selected via those indices. There
are two types of indices,
+
+ 1. Integer indices that represents the real indices in the vector,
`setIndices()`;
+
+ 2. String indices that represents the names of features in the vector,
`setNames()`.
+
+Specify by integer and string are both acceptable, moreover, you can use
integer index and string name simultaneously. At least one feature must be
selected. Duplicate features are not allowed, so there can be no overlap
between selected indices and names. Note that if names of features are
selected, an exception will be threw out when encountering with empty input
attributes.
--- End diff --
nit: ***Specification*** by integer and string are both acceptable***.
M***oreover,
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