如何动态填充数据框的选择子句?给出AnalysisException [英] how to populate select clause of dataframe dynamically? giving AnalysisException

问题描述

我正在使用spark-sql 2.4.1和Java 8.

I am Using spark-sql 2.4.1 and java 8.

 val country_df = Seq(
    ("us",2001),
    ("fr",2002),
    ("jp",2002),
    ("in",2001),
    ("fr",2003),
    ("jp",2002),
    ("in",2003)
    ).toDF("country","data_yr")

> val col_df = country_df.select("country").where($"data_yr" === 2001)

    val data_df = Seq(
    ("us_state_1","fr_state_1" ,"in_state_1","jp_state_1"),
    ("us_state_2","fr_state_2" ,"in_state_2","jp_state_1"),
    ("us_state_3","fr_state_3" ,"in_state_3","jp_state_1")
    ).toDF("us","fr","in","jp")

> data_df.select("us","in").show()

如何从给定年份的country_df中动态填充(data_df的)select子句?

how to populate this select clause (of data_df) dynamically , from the country_df for given year ?

即从第一个数据帧，我将获得column的值，这些是 我需要从第二个datafame中选择的列.怎么会这样 完成了吗?

i.e. From first dataframe , i will get values of column , those are the columns i need to select from second datafame. How can this be done ?

尝试过:

List<String> aa = col_df.select(functions.lower(col("data_item_code"))).map(row -> row.mkString(" ",", "," "), Encoders.STRING()).collectAsList();
 data_df.select(aa.stream().map(s -> new Column(s)).toArray(Column[]::new));

错误:

.AnalysisException: cannot resolve '` un `' given input columns: [abc,.....all columns ...]

那么这里有什么问题，以及如何解决?

So what is wrong here , and how to fix this ?

推荐答案

您可以尝试以下代码.

从第一个数据集中选择列名.

Select the column name from the first dataset.

List<String> columns = country_df.select("country").where($"data_yr" === 2001).as(Encoders.STRING()).collectAsList();

在第二个数据集中的selectexpr中使用列名.

Use the column names in selectexpr in second dataset.

public static Seq<String> convertListToSeq(List<String> inputList) {
        return JavaConverters.asScalaIteratorConverter(inputList.iterator()).asScala().toSeq();
}


//using selectExpr
data_df.selectExpr(convertListToSeq(columns)).show(true);

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