How to delete columns in pyspark dataframe

问题:

>>> a
DataFrame[id: bigint, julian_date: string, user_id: bigint]
>>> b
DataFrame[id: bigint, quan_created_money: decimal(10,0), quan_created_cnt: bigint]
>>> a.join(b, a.id==b.id, 'outer')
DataFrame[id: bigint, julian_date: string, user_id: bigint, id: bigint, quan_created_money: decimal(10,0), quan_created_cnt: bigint]

There are two id: bigint and I want to delete one. How can I do?

回答1:

Reading the Spark documentation I found an easier solution.

Since version 1.4 of spark there is a function drop(col) which can be used in pyspark on a dataframe.

You can use it in two ways

1. df.drop('age').collect()
2. df.drop(df.age).collect()

Pyspark Documentation - Drop

回答2:

An easy way to do this is to user "select" and realize you can get a list of all columns for the dataframe, df, with df.columns

drop_list = ['a column', 'another column', ...]

df.select([column for column in df.columns if column not in drop_list])

回答3:

You could either explicitly name the columns you want to keep, like so:

keep = [a.id, a.julian_date, a.user_id, b.quan_created_money, b.quan_created_cnt]

Or in a more general approach you'd include all columns except for a specific one via a list comprehension. For example like this (excluding the id column from b):

keep = [a[c] for c in a.columns] + [b[c] for c in b.columns if c != 'id']

Finally you make a selection on your join result:

d = a.join(b, a.id==b.id, 'outer').select(*keep)

回答4:

Adding to @Patrick's answer, you can use the following to drop multiple columns

columns_to_drop = ['id', 'id_copy']
df = df.drop(*columns_to_drop)

回答5:

You can use two way:

1: You just keep the necessary columns:

drop_column_list = ["drop_column"]
df = df.select([column for column in df.columns if column not in drop_column_list])  

2: This is the more elegant way.

df = df.drop("col_name")

You should avoid the collect() version, because it will send to the master the complete dataset, it will take a big computing effort!

回答6:

Maybe a little bit off topic, but here is the solution using Scala. Make an Array of column names from your oldDataFrame and delete the columns that you want to drop ("colExclude"). Then pass the Array[Column] to select and unpack it.

val columnsToKeep: Array[Column] = oldDataFrame.columns.diff(Array("colExclude"))
                                               .map(x => oldDataFrame.col(x))
val newDataFrame: DataFrame = oldDataFrame.select(columnsToKeep: _*)