如何获取列的名称或更改现有列的名称？

Question

我的任务是构建一个函数“RemovePercentration”，该函数去除标点符号，从而通过此测试：

# TEST Capitalization and punctuation (4b)
testPunctDF = sqlContext.createDataFrame([(" The Elephant's 4 cats. ",)])
testPunctDF.show()
Test.assertEquals(testPunctDF.select(removePunctuation(col('_1'))).first()[0],
                  'the elephants 4 cats',
                  'incorrect definition for removePunctuation function')

这是我设法写的

def removePunctuation(column):
    """Removes punctuation, changes to lower case, and strips leading and trailing spaces.

    Note:
        Only spaces, letters, and numbers should be retained.  Other characters should should be
        eliminated (e.g. it's becomes its).  Leading and trailing spaces should be removed after
        punctuation is removed.

    Args:
        column (Column): A Column containing a sentence.

    Returns:
        Column: A Column named 'sentence' with clean-up operations applied.
    """

    return lower(trim(regexp_replace("column_name", "[\W_]+"," "))).alias("sentence");

但我仍然无法使函数regexp_替换为使用别名“句子”。我得到这个错误：

AnalysisException: u"cannot resolve 'sentence' given input columns: [_1];"

Answer 1

令人惊讶的是，我只能以regexp_replace()参数而不是列名传递列对象