Show all pyspark columns after group and agg - pyspark

Question

I wish to groupby a column and then find the max of another column. Lastly, show all the columns based on this condition. However, when I used my codes, it only show 2 columns and not all of it.
# Normal way of creating dataframe in pyspark
sdataframe_temp = spark.createDataFrame([
(2,2,'0-2'),
(2,23,'22-24')],
['a', 'b', 'c']
)
sdataframe_temp2 = spark.createDataFrame([
(4,6,'4-6'),
(5,7,'6-8')],
['a', 'b', 'c']
)
# Concat two different pyspark dataframe
sdataframe_union_1_2 = sdataframe_temp.union(sdataframe_temp2)
sdataframe_union_1_2_g = sdataframe_union_1_2.groupby('a').agg({'b':'max'})
sdataframe_union_1_2_g.show()
output:
+---+------+
| a|max(b)|
+---+------+
| 5| 7|
| 2| 23|
| 4| 6|
+---+------+
Expected output:
+---+------+-----+
| a|max(b)| c |
+---+------+-----+
| 5| 7|6-8 |
| 2| 23|22-24|
| 4| 6|4-6 |
+---+------+---+

Answer 1

You can use a Window function to make it work:
Method 1: Using Window function
import pyspark.sql.functions as F
from pyspark.sql.window import Window
w = Window().partitionBy("a").orderBy(F.desc("b"))
(sdataframe_union_1_2
.withColumn('max_val', F.row_number().over(w) == 1)
.where("max_val == True")
.drop("max_val")
.show())
+---+---+-----+
| a| b| c|
+---+---+-----+
| 5| 7| 6-8|
| 2| 23|22-24|
| 4| 6| 4-6|
+---+---+-----+
Explanation
Window functions are useful when we want to attach a new column to the existing set of columns.
In this case, I tell Window function to groupby partitionBy('a') column and sort the column b in descending order F.desc(b). This make the first value in b in each group its max value.
Then we use F.row_number() to filter the max values where row number equals 1.
Finally, we drop the new column since it is not being used after filtering the data frame.
Method 2: Using groupby + inner join
f = sdataframe_union_1_2.groupby('a').agg(F.max('b').alias('b'))
sdataframe_union_1_2.join(f, on=['a','b'], how='inner').show()
+---+---+-----+
| a| b| c|
+---+---+-----+
| 2| 23|22-24|
| 5| 7| 6-8|
| 4| 6| 4-6|
+---+---+-----+