Removing rows from a data.frame with -grep removes all rows if no matches are found (-- how to preve-CodePudding

I have a data frame that gets updated frequently, and there are some rows that need to be removed from it if certain strings are found in them. I have done that previously using -grep to remove the rows containing the string in question, eg:

dataframe[-grep('some string', dataframe$column),]

However, at times that string doesn't appear in the dataframe, in which case the -grep is returning an empty dataframe. Here's a minimal reproducible example:

> test.df<-data.frame(number=c(1:10), letter=letters[1:10])

> test.df
   number letter
1       1      a
2       2      b
3       3      c
4       4      d
5       5      e
6       6      f
7       7      g
8       8      h
9       9      i
10     10      j

> test.df[-grep('h', test.df$letter),]
   number letter
1       1      a
2       2      b
3       3      c
4       4      d
5       5      e
6       6      f
7       7      g
9       9      i
10     10      j

> test.df[-grep('k', test.df$letter),]
[1] number letter
<0 rows> (or 0-length row.names)

I could wrap the 'test.df[-grep...' in an 'if' test to check if the search string is found prior to removing it, eg:

if(any(grepl('k',test.df$letter))){test.df<-test.df[-grep('k', test.df$letter),]}

...but it seems to me that this should be implicit in the -grep command. Is there a better (more efficient) way to accomplish row removal that doesn't threaten to remove all my data if the search string is absent from the data frame?

CodePudding user response：

Using grepl you could do:

test.df <- data.frame(number = c(1:10), letter = letters[1:10])

test.df[!grepl("h", test.df$letter), ]
#>    number letter
#> 1       1      a
#> 2       2      b
#> 3       3      c
#> 4       4      d
#> 5       5      e
#> 6       6      f
#> 7       7      g
#> 9       9      i
#> 10     10      j

test.df[!grepl("k", test.df$letter), ]
#>    number letter
#> 1       1      a
#> 2       2      b
#> 3       3      c
#> 4       4      d
#> 5       5      e
#> 6       6      f
#> 7       7      g
#> 8       8      h
#> 9       9      i
#> 10     10      j

^{Created on 2023-01-19 with reprex v2.0.2}