如何消除 PySpark DataFrame 列中条目的第一个字符？

Question

So I have a given PySpark DataFrame, say df , looking like below:

df.show()
+--------------------+-------------------+
|              series|          value    |
+--------------------+-------------------+
|     XXXX-AAAA      |          1        |
|     XXXX-BB        |          2        |
|     XXXX-CCCCC     |          3        |
+--------------------+-------------------+

In the series column, I would like to get rid of the XXXX- substring (ie length of 5 characters), which is the same for each single entry of that column, thus obtaining the followind DataFrame, say df2 :

df2.show()
+--------------------+-------------------+
|              series|          value    |
+--------------------+-------------------+
|        AAAA        |          1        |
|        BB          |          2        |
|        CCCCC       |          3        |
+--------------------+-------------------+

I have tried to use the substr method but, as you can imagine, the challenge lies in the variability of the length of each entry in the series column. The code that I have tried is the following:

from pyspark.sql.functions import length

df2 = df.withColumn('series_truncated', df.timestamp.substr(5, length(df.series)))
df2 = df2.drop('series')
df2 = df2.withColumnRenamed("series_truncated", "series")
df.show()

Together with the associated error:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-14-6585c018cd92> in <module>
      3 #print(length(df.series))
      4 #df_test.show()
----> 5 df = df.withColumn('series_truncated', df.timestamp.substr(15, length(df.series)))  # Eliminate the first 14 digits of the timestamp column
      6 
      7 #df_test = df.withColumn('length_series', length(df.series))

/usr/local/spark/python/pyspark/sql/column.py in substr(self, startPos, length)
    417                 .format(
    418                     startPos_t=type(startPos),
--> 419                     length_t=type(length),
    420                 ))
    421         if isinstance(startPos, int):

TypeError: startPos and length must be the same type. Got <class 'int'> and <class 'pyspark.sql.column.Column'>, respectively.

Does anyone know how this can be solved?

Many thanks in advance,

Marioanzas

Answer 1

Two ways:

import pyspark.sql.functions as F

df.withColumn('series', F.regexp_extract('series', 'XXXX-(.*)$', 1)).show()
+------+-----+
|series|value|
+------+-----+
|  AAAA|    1|
|    BB|    2|
| CCCCC|    3|
+------+-----+

Or

import pyspark.sql.functions as F

df.withColumn('series', F.expr('substring(series, 6, length(series) - 5)')).show()
+------+-----+
|series|value|
+------+-----+
|  AAAA|    1|
|    BB|    2|
| CCCCC|    3|
+------+-----+

Note that the substring function in Pyspark API does not accept column objects as arguments, but the Spark SQL API does, so you need to use F.expr in the second method.

Answer 2

from pyspark.sql.functions import substring, length, col, expr
df.withColumn('series',expr('substring(series, 6, length(series))'))

Answer 3

You could also use right function along with lenght to get the rightmost length(series)-5 caracters from the string:

df.withColumn("series", expr("right(series, length(series)-5)")).show()

#+------+-----+
#|series|value|
#+------+-----+
#|  AAAA|    1|
#|    BB|    2|
#| CCCCC|    3|
#+------+-----+

Or simplyreplace XXXX- by empty string '' :

df.withColumn("series", expr("replace(series, 'XXXX-', '')")).show()

Note however that replace will get rid of all XXXX- occurrences not only at the beginning of the string.