Delete rows containing specific strings in R

Question

I would like to exclude lines containing a string "REVERSE", but my lines do not match exactly with the word, just contain it.

My input data frame:

   Value   Name 
    55     REVERSE223   
    22     GENJJS
    33     REVERSE456
    44     GENJKI

My expected output:

   Value   Name 
    22     GENJJS
    44     GENJKI

Crotchet

Answer 1

This should do the trick:

df[- grep("REVERSE", df$Name),]

Or a safer version would be:

df[!grepl("REVERSE", df$Name),]

Md

What do you mean by "safer"? – Telega

What if I want to delete the rows containing a "(". The following does not seem to work: df[!grepl("(", df$Name),] – Deformity

@Deformity The grepl function uses regular expressions for the match, which have a syntax where ( is meaningful. If you set the named parameter fixed = TRUE then grepl will perform a literal match without using regular expressions, which should work for your use case. – Chlorella

@JasonMeloHall minus (-) operator does use negative indexing and negation (!) operator uses logical indexing so negation operator is safer than minus(-) – Fairleigh

How could you modify this to also delete the row above the row that contains the matching string? – Justiceship

Thanks a lot - googled for about 1h before I found your answer. Works brilliant. – Drawbridge

Hi guys, I tried the code in my contigency table making, although I save my dataframe as a new data, the filtered rows are still kept as a level with "0" entries. how do I ask it to completely delete the rows in the new dataframe? – Pieter

Answer 2

You could use dplyr::filter() and negate a grepl() match:

library(dplyr)

df %>% 
  filter(!grepl('REVERSE', Name))

Or with dplyr::filter() and negating a stringr::str_detect() match:

library(stringr)

df %>% 
  filter(!str_detect(Name, 'REVERSE'))

Stalactite

This question asks for many strings. So what happens if you want to remove multiple strings i.e. remove.list <- c("REVERSE", "FOO", "BAR, "JJ") – Occupy

Sure, you can do create the list like this: remove.list <- paste(c("REVERSE", "FOO", "BAR", "JJ"), collapse = '|') And then filter like this: df %>% filter(!grepl(remove.list, Name)) df %>% filter(!str_detect(Name, remove.list)) – Stalactite

How to drop rows based in strings present in two columns, like filter(!grepl('REVERSE', Name & 'BAR', Name)), I got the following error trying this way. ! operations are possible only for numeric, logical or complex types – Parsnip

Answer 3

Actually I would use:

df[ grep("REVERSE", df$Name, invert = TRUE) , ]

This will avoid deleting all of the records if the desired search word is not contained in any of the rows.

Rosie

Answer 4

You can use stri_detect_fixed function from stringi package

stri_detect_fixed(c("REVERSE223","GENJJS"),"REVERSE")
[1]  TRUE FALSE

Depress

Answer 5

You can use this function if it's multiple string df[!grepl("REVERSE|GENJJS", df$Name),]

Snapp

Answer 6

You can use it in the same datafram (df) using the previously provided code

df[!grepl("REVERSE", df$Name),]

or you might assign a different name to the datafram using this code

df1<-df[!grepl("REVERSE", df$Name),]

Steal

Answer 7

A late answer building on BobD59's and hidden-layer's responses.

This removes multiple specific strings, whilst avoiding deleting all of the records if the desired search word is not contained in any of the rows.

df1 <-
   df[!grepl("REVERSE|GENJJS", df$Name), (invert = TRUE), ]

Aftersensation