如何用Spark dataframe中的单行空值替换在一列中重复的多行

from pyspark.sql import SparkSession
from pyspark.sql.functions import col, when

spark = SparkSession.builder.getOrCreate()

data = [(1, "A"), (2, "B"), (3, "A"), (4, "C"), (5, "A"), (6, "B"), (7, "A")]
df = spark.createDataFrame(data, ["id", "value"])

df_count = df.groupBy("value").count()
df_result = df.join(df_count, "value", "left_outer") \
              .withColumn("value", when(col("count") > 1, None).otherwise(col("value"))) \
              .drop("count")

df_result.show()