[MINOR] Fix Typos 'an -> a'

## What changes were proposed in this pull request?

`an -> a`

Use cmds like `find . -name '*.R' | xargs -i sh -c "grep -in ' an [^aeiou]' {} && echo {}"` to generate candidates, and review them one by one.

## How was this patch tested?
manual tests

Author: Zheng RuiFeng <ruifengz@foxmail.com>

Closes #13515 from zhengruifeng/an_a.

2 files changed, 3 insertions, 3 deletions

diff --git a/python/pyspark/ml/classification.py b/python/pyspark/ml/classification.py
index 7710fdf2e2..77badebeb4 100644
--- a/python/pyspark/ml/classification.py
+++ b/python/pyspark/ml/classification.py
@@ -351,7 +351,7 @@ class BinaryLogisticRegressionSummary(LogisticRegressionSummary):
     def roc(self):
         """
         Returns the receiver operating characteristic (ROC) curve,
-        which is an Dataframe having two fields (FPR, TPR) with
+        which is a Dataframe having two fields (FPR, TPR) with
         (0.0, 0.0) prepended and (1.0, 1.0) appended to it.
 
         .. seealso:: `Wikipedia reference \
@@ -380,7 +380,7 @@ class BinaryLogisticRegressionSummary(LogisticRegressionSummary):
     @since("2.0.0")
     def pr(self):
         """
-        Returns the precision-recall curve, which is an Dataframe
+        Returns the precision-recall curve, which is a Dataframe
         containing two fields recall, precision with (0.0, 1.0) prepended
         to it.
 
diff --git a/python/pyspark/ml/pipeline.py b/python/pyspark/ml/pipeline.py
index eb6d3310d6..0777527134 100644
--- a/python/pyspark/ml/pipeline.py
+++ b/python/pyspark/ml/pipeline.py
@@ -42,7 +42,7 @@ class Pipeline(Estimator, MLReadable, MLWritable):
     stage. If a stage is a :py:class:`Transformer`, its
     :py:meth:`Transformer.transform` method will be called to produce
     the dataset for the next stage. The fitted model from a
-    :py:class:`Pipeline` is an :py:class:`PipelineModel`, which
+    :py:class:`Pipeline` is a :py:class:`PipelineModel`, which
     consists of fitted models and transformers, corresponding to the
     pipeline stages. If there are no stages, the pipeline acts as an
     identity transformer.