SparklyR separate one Spark DataFrame column into two columns

问题

I have a dataframe containing a column named COL which is structured in this way:

VALUE1###VALUE2

The following code is working

library(sparklyr)
library(tidyr)
library(dplyr)
mParams<- collect(filter(input_DF, TYPE == ('MIN')))
mParams<- separate(mParams, COL, c('col1','col2'), '\\###', remove=FALSE)

If I remove the collect, I get this error:

Error in UseMethod("separate_") : 
  no applicable method for 'separate_' applied to an object of class "c('tbl_spark', 'tbl_sql', 'tbl_lazy', 'tbl')"

Is there any alternative to achieve what I want, but without collecting everything on my spark driver?

回答1:

You can use ft_regex_tokenizer followed by sdf_separate_column.

ft_regex_tokenizer will split a column into a vector type, based on a regex. sdf_separate_column will split this into multiple columns.

mydf %>% 
    ft_regex_tokenizer(input_col="mycolumn", output_col="mycolumnSplit", pattern=";") %>% 
    sdf_separate_column("mycolumnSplit", into=c("column1", "column2")

UPDATE: in recent versions of sparklyr, the parameters input.col and output.col have been renamed to input_col and output_col, respectively.

回答2:

Sparklyr version 0.5 has just been released, and it contains the ft_regex_tokenizer() function that can do that:

A regex based tokenizer that extracts tokens either by using the provided regex pattern to split the text (default) or repeatedly matching the regex (if gaps is false).

library(dplyr)
library(sparklyr)
ft_regex_tokenizer(input_DF, input.col = "COL", output.col = "ResultCols", pattern = '\\###')

The splitted column "ResultCols" will be a list.

来源：https://stackoverflow.com/questions/41810015/sparklyr-separate-one-spark-dataframe-column-into-two-columns