Question

在Spark DataFrame中，我们有一个select方法，其第二个参数为varargs：

  @scala.annotation.varargs
  def select(col: String, cols: String*): DataFrame = 
        select((col +: cols).map(Column(_)) : _*)

我想使用select：

调用Sequence

val ProductCols = Seq("prdct_id", "prdct_tag")

首选项将按以下方式调用：

myDataFrame.select(ProductCols: _*)

但是，这并没有解决上面显示的方法，因此使用了以下内容：

myDataFrame.select(ProductCols.head, ProductCols.tail: _*)

有没有办法只发送ProductCols一次 - 而varargs会接受它？

Answer 1

您应该将String包装到列：

import MySQLdb
import base64
db = MySQLdb.connect(host="localhost",    # your host, usually localhost
                     user="test",         # your username
                     passwd="test",  # your password
                     db="test")
cur = db.cursor()


cur.execute("SELECT * FROM attachments")

#looping through row 4 where all blobs are located

for row in cur.fetchall():
    blob_read = row[4]

#(error happen here while decoding)

    decoding = blob_read.decode('base64')
    print '<img src="data:image/jpg;base64,"'+ decoding + '/>'

    filename = row[2]

#(extracted the files to test if images are corrupted; they are not)

       with open(filename, 'wb') as output_file:
        output_file.write(blob_read)

db.close()

也写Df.select(cols.map(x => col(x)) :_*)

提供序列作为接受varargs的方法的参数

1 个答案: