Question

我已经创建了一个如图所示的数据框

   import ast
   from pyspark.sql.functions import udf
   values = [(u'['2','4','713',10),(u'['12','245']',20),(u'['101','12']',30)]
   df = sqlContext.createDataFrame(values,['list','A'])
   df.show()
   +-----------------+---+
   |             list|  A|
   +-----------------+---+
   |u'['2','4','713']| 10|
   |  u' ['12','245']| 20|
   |  u'['101','12',]| 30|
   +-----------------+---+

**How can I convert the above dataframe such that each element in the list is a float and is within a proper list**
I tried the below one :

   def df_amp_conversion(df_modelamp):
      string_list_to_list = udf(lambda row: ast.literal_eval(str(row)))
      df_modelamp  = df_modelamp.withColumn('float_list',string_list_to_list(col("list")))

   df2 = amp_conversion(df)

但是数据保持不变，没有变化。我不想将数据框转换为熊猫或使用收集，因为它占用大量内存。如果可能，请尝试为我提供最佳解决方案。我正在使用pyspark

Answer 1

那是因为您忘记了类型

udf(lambda row: ast.literal_eval(str(row)), "array<integer>")

尽管这样会更有效：

from pyspark.sql.functions import rtrim, ltrim, split 

df = spark.createDataFrame(["""u'[23,4,77,890,4]"""], "string").toDF("list")

df.select(split(
    regexp_replace("list", "^u'\\[|\\]$", ""), ","
).cast("array<integer>").alias("list")).show()

# +-------------------+
# |               list|
# +-------------------+
# |[23, 4, 77, 890, 4]|
# +-------------------+

Answer 2

我可以在python 3中创建真正的结果，而对函数df_amp_conversion的定义稍作更改。您没有返回df_modelamp的值！这段代码对我来说正常工作：

import ast
from pyspark.sql.functions import udf, col
values = [(u"['2','4','713']",10),(u"['12','245']",20),(u"['101','12']",30)]

df = sqlContext.createDataFrame(values,['list','A'])


def df_amp_conversion(df_modelamp):
    string_list_to_list = udf(lambda row: ast.literal_eval(str(row)))
    df_modelamp  = df_modelamp.withColumn('float_list',string_list_to_list(col("list")))
    return df_modelamp

df2 = df_amp_conversion(df)
df2.show()

#    +---------------+---+-----------+
#    |           list|  A| float_list|
#    +---------------+---+-----------+
#    |['2','4','713']| 10|[2, 4, 713]|
#    |   ['12','245']| 20|  [12, 245]|
#    |   ['101','12']| 30|  [101, 12]|
#    +---------------+---+-----------+

如何将数据帧的pyspark列中包含的Unicode列表转换为浮点列表？

2 个答案: