[SPARK-35738][PYTHON] Support 'y' properly in DataFrame with non-numeric columns with plots

### What changes were proposed in this pull request?

This PR proposes to port the fix databricks/koalas#2172.

```python
ks.DataFrame({'a': [1, 2, 3], 'b':["a", "b", "c"], 'c': [4, 5, 6]}).plot(kind='hist', x='a', y='c', bins=200)
```

**Before:**

```
pyspark.sql.utils.AnalysisException: cannot resolve 'least(min(a), min(b), min(c))' due to data type mismatch: The expressions should all have the same type, got LEAST(bigint, string, bigint).;
'Aggregate [unresolvedalias(least(min(a#1L), min(b#2), min(c#3L)), Some(org.apache.spark.sql.Column$$Lambda$1556/0x0000000800d9484042fb0cc1)), unresolvedalias(greatest(max(a#1L), max(b#2), max(c#3L)), Some(org.apache.spark.sql.Column$$Lambda$1556/0x0000000800d9484042fb0cc1))]
+- Project [a#1L, b#2, c#3L]
   +- Project [__index_level_0__#0L, a#1L, b#2, c#3L, monotonically_increasing_id() AS __natural_order__#8L]
      +- LogicalRDD [__index_level_0__#0L, a#1L, b#2, c#3L], false
```

**After:**

```python
Figure({
    'data': [{'hovertemplate': 'variable=a<br>value=%{text}<br>count=%{y}',
              'name': 'a',
...
```

### Why are the changes needed?

To match the behaviour with panadas' and allow users to set `x` and `y` in the DataFrame with non-numeric columns.

### Does this PR introduce _any_ user-facing change?

No to end users since the changes is not released yet. Yes to dev as described before.

### How was this patch tested?

Manually tested, added a test and tested in notebooks:

![Screen Shot 2021-06-11 at 9 11 25 PM](https://user-images.githubusercontent.com/6477701/121686038-a47a1b80-cafb-11eb-8f8e-8d968db7ebef.png)

![Screen Shot 2021-06-11 at 9 48 58 PM](https://user-images.githubusercontent.com/6477701/121688858-e22c7380-cafe-11eb-9d0a-adcbe560030f.png)

Closes apache#32884 from HyukjinKwon/fix-hist-plot.

Authored-by: Hyukjin Kwon <[email protected]>
Signed-off-by: Hyukjin Kwon <[email protected]>

Author: HyukjinKwon

python/pyspark/pandas/plot/plotly.py

@@ -73,8 +73,14 @@ def plot_pie(data: Union["ps.DataFrame", "ps.Series"], **kwargs):
 
 def plot_histogram(data: Union["ps.DataFrame", "ps.Series"], **kwargs):
     import plotly.graph_objs as go
+    import pyspark.pandas as ps
 
     bins = kwargs.get("bins", 10)
+    y = kwargs.get("y")
+    if y and isinstance(data, ps.DataFrame):
+        # Note that the results here are matched with matplotlib. x and y
+        # handling is different from pandas' plotly output.
+        data = data[y]
     psdf, bins = HistogramPlotBase.prepare_hist_data(data, bins)
     assert len(bins) > 2, "the number of buckets must be higher than 2."
     output_series = HistogramPlotBase.compute_hist(psdf, bins)

python/pyspark/pandas/tests/plot/test_frame_plot_matplotlib.py

@@ -411,6 +411,19 @@ def check_hist_plot(pdf, psdf):
             bin2 = self.plot_to_base64(ax2)
             self.assertEqual(bin1, bin2)
 
+            non_numeric_pdf = self.pdf1.copy()
+            non_numeric_pdf.c = ["a", "b", "c", "d", "e", "f", "g", "h", "i", "j", "k"]
+            non_numeric_psdf = ps.from_pandas(non_numeric_pdf)
+            ax1 = non_numeric_pdf.plot.hist(
+                x=non_numeric_pdf.columns[0], y=non_numeric_pdf.columns[1], bins=3
+            )
+            bin1 = self.plot_to_base64(ax1)
+            ax2 = non_numeric_psdf.plot.hist(
+                x=non_numeric_pdf.columns[0], y=non_numeric_pdf.columns[1], bins=3
+            )
+            bin2 = self.plot_to_base64(ax2)
+            self.assertEqual(bin1, bin2)
+
         pdf1 = self.pdf1
         psdf1 = self.psdf1
         check_hist_plot(pdf1, psdf1)