我有两个按某一列排序的数据框,这也是连接键。
是否可以合并这两个数据帧,并在 O(n+m) 中返回一个已排序的数据帧?我不在乎它是否不是并行完成的。我的数据太多(40 亿 + 2000 万行),我无法使用简单的
events.join(t_status, on='t').sort('t')
您可以在线性时间内O(n+m)
合并已排序的数据帧,如下所示:
from pyspark.sql import SparkSession
spark = SparkSession.builder.getOrCreate()
# Example dataframes sorted by "key" in ascending order
df1 = spark.createDataFrame([(1, "A"), (3, "C"), (5, "E")], ["key", "value"])
df2 = spark.createDataFrame([(2, "B"), (4, "D"), (6, "F")], ["key", "value"])
rdd1 = df1.rdd
rdd2 = df2.rdd
def merge_sorted_rdds(rdd1, rdd2):
# Get iterators for both RDDs
iter1 = rdd1.collect()
iter2 = rdd2.collect()
i, j = 0, 0
merged_result = []
# Merge the two sorted RDDs
while i < len(iter1) and j < len(iter2):
if iter1[i][0] < iter2[j][0]:
merged_result.append(iter1[i])
i += 1
else:
merged_result.append(iter2[j])
j += 1
while i < len(iter1):
merged_result.append(iter1[i])
i += 1
while j < len(iter2):
merged_result.append(iter2[j])
j += 1
return merged_result
merged_data = merge_sorted_rdds(rdd1, rdd2)
merged_df = spark.createDataFrame(merged_data, ["key", "value"])
merged_df.show()
# Output:
# +---+-----+
# |key|value|
# +---+-----+
# | 1| A|
# | 2| B|
# | 3| C|
# | 4| D|
# | 5| E|
# | 6| F|
# +---+-----+