如何计算pyspark数据帧的协方差矩阵？

from pyspark.sql import SparkSession
from pyspark.ml.feature import VectorAssembler
from pyspark.ml.stat import Correlation

spark = SparkSession.builder.appName("CovarianceMatrix").getOrCreate()

assembler = VectorAssembler(inputCols=df.columns, outputCol="features")
df_vector = assembler.transform(df).select("features")

cov_matrix = Correlation.corr(df_vector, "features").head()[0]

print(cov_matrix)