Removing data from one dataframe that exists in another dataframe R

Question

I want to remove data from a dataframe that is present in another dataframe. Let me give an example:

letters<-c(\'a\',\'b\',\'c\',\'d\',\'e\')
numbers<-c(1         


        

Answer 1

Base R Solution

list_one[!list_one$letters %in% list_two$letters2,]

gives you:

  letters numbers
2       b       2
5       e       5

Explanation:

> list_one$letters %in% list_two$letters2
[1]  TRUE FALSE  TRUE  TRUE FALSE

This gives you a vector of LENGTH == length(list_one$letters) with TRUE/FALSE Values. ! negates this vector. So you end up with FALSE/TRUE values if the value is present in list_two$letters2.

If you have questions about how to select rows from a data.frame enter

?`[.data.frame`

to the console and read it.

Answer 2

A dplyr solution

library(dplyr)

list_one %>% anti_join(list_two)

Answer 3

Answer is response to your edit: " so I really can't use the negative expression".

I guess one of the most efficient ways to do this is using data.table as follows:

require(data.table)
setDT(list_one)
setDT(list_two)
list_one[!list_two, on=c(letters = "letters2")]

Or

require(data.table)
setDT(list_one, key = "letters")
setDT(list_two, key = "letters2")
list_one[!letters2]

(Thanks to Frank for the improvement)

Result:

   letters numbers
1:       b       2
2:       e       5

Have a look at ?"data.table" and Quickly reading very large tables as dataframes in R on why to use data.table::freadto read the csv-files in the first place.

BTW: If you have letters2 instead of list_two you can use

list_one[!J(letters2)]