Github user MLnick commented on a diff in the pull request:

    https://github.com/apache/spark/pull/20257#discussion_r161989945
  
    --- Diff: docs/ml-features.md ---
    @@ -777,17 +777,17 @@ for more details on the API.
     
     ## OneHotEncoder (Deprecated since 2.3.0)
     
    -Because this existing `OneHotEncoder` is a stateless transformer, it is 
not usable on new data where the number of categories may differ from the 
training data. In order to fix this, a new `OneHotEncoderEstimator` was created 
that produces an `OneHotEncoderModel` when fitting. For more detail, please see 
the JIRA ticket (https://issues.apache.org/jira/browse/SPARK-13030).
    +Because this existing `OneHotEncoder` is a stateless transformer, it is 
not usable on new data where the number of categories may differ from the 
training data. In order to fix this, a new `OneHotEncoderEstimator` was created 
that produces an `OneHotEncoderModel` when fitting. For more detail, please see 
[SPARK-13030](https://issues.apache.org/jira/browse/SPARK-13030).
     
    -`OneHotEncoder` has been deprecated in 2.3.0 and will be removed in 3.0.0. 
Please use [OneHotEncoderEstimator](ml-features.html#onehotencoderestimator) 
for one-hot encoding instead.
    +`OneHotEncoder` has been deprecated in 2.3.0 and will be removed in 3.0.0. 
Please use [OneHotEncoderEstimator](ml-features.html#onehotencoderestimator) 
instead.
     
     ## OneHotEncoderEstimator
     
    -[One-hot encoding](http://en.wikipedia.org/wiki/One-hot) maps a column of 
label indices to a column of binary vectors, with at most a single one-value. 
This encoding allows algorithms which expect continuous features, such as 
Logistic Regression, to use categorical features. For string type input data, 
it is common to encode categorical features using 
[StringIndexer](ml-features.html#stringindexer) first.
    +[One-hot encoding](http://en.wikipedia.org/wiki/One-hot) maps a column of 
label indices to a column of binary vectors, and each output binary vector 
includes at most a single one-value. This encoding allows algorithms which 
expect continuous features, such as Logistic Regression, to use categorical 
features. For string type input data, it is common to encode categorical 
features using [StringIndexer](ml-features.html#stringindexer) first.
     
    -`OneHotEncoderEstimator` can handle multi-column. By specifying multiple 
input columns, it returns a one-hot-encoded output vector column for each input 
column.
    +`OneHotEncoderEstimator` can transform multiple columns, returning a 
one-hot-encoded output vector column for each input column.
    --- End diff --
    
    Perhaps we should add a note about vector assembling, something like "It is 
common to merge these vectors into a single feature vector using 
`VectorAssembler`"?


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