[英]Using the columns of one dataframe in another dataframe
I am trying to read the data from one dataframe and use it in another.我正在尝试从一个数据框中读取数据并在另一个数据框中使用它。 How can I do it gracefully?
我怎样才能优雅地做到这一点?
val query = s"select distinct p_id, lower(regexp_replace(p_id,'[^a-zA-Z0-9]+','_')) as p_id_formatted, lower(regexp_extract(f_id,'^([^\\.]+)\\.?',1)) as f_id_formatted, column_name from default.rc_pcoders"
val run_query = sql(query)
val table_name = run_query.select(concat(lit("nepp"), lit("_"),$"p_id_formatted", lit("_") ,$"f_id_formatted ").alias("tablename"),$"column_name")
This gives me below output, which essentially represents a tablename这给了我下面的输出,它基本上代表一个表名
+------------------+-----------+
|tablename |column_name|
+------------------+-----------+
|nepp_148hl16011_cm|cmtrt |
|nepp_148hl16011_mh|mhaspe |
|nepp_148hl16011_ae|aeputt |
+------------------+-----------+
How can I get the column names from each of these tables?如何从每个表中获取列名? Something like (below query doesn't work though)
类似的东西(虽然下面的查询不起作用)
val whole_query = sql("show columns in "table_name.tablename"")
First, collect all the names of the tables to load:首先,收集要加载的所有表的名称:
val tableNames = df.collect().map(row => row.getAs[String]("tablename")).toSeq
Second, get the references to the respective DataFrames, associate them with their column names其次,获取对相应 DataFrame 的引用,将它们与它们的列名相关联
val sqlCtx: SQLContext = // your SQL context ref
val dfToColumns = tableNames.map(table => {
val columnNames = sqlCtx.table(table).schema.fieldNames.toSeq
(table, columnNames)
}).toMap
dfToColumns
is a Map[String, Seq[String]]
with DataFrame names as keys and Seqs of their respective column names as values. dfToColumns
是一个Map[String, Seq[String]]
以 DataFrame 名称作为键,将它们各自列名称的 Seqs 作为值。
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