Using grep in R to delete rows from a data.frame

user_844570 0
Viewed 22006

I have a dataframe such as this one:

d <- data.frame(x=1,
                y=1:10,
                z=c("apple","pear","banana","A","B","C","D","E","F","G"),
                stringsAsFactors = FALSE)

I'd like to delete some rows from this dataframe, depending on the content of column z:

new_d <- d[-grep("D",d$z),]

This works fine; row 7 is now deleted:

    new_d
     x  y      z
  1  1  1  apple
  2  1  2   pear
  3  1  3 banana
  4  1  4      A
  5  1  5      B
  6  1  6      C
  8  1  8      E
  9  1  9      F
  10 1 10      G

However, when I use grep to search for content that is not present in column z, it seems to delete all content of the dataframe:

new_d <- d[-grep("K",d$z),]
new_d
# [1] x y z
# <0 rows> (or 0-length row.names)

I would like to search and delete rows in this or another way, even if the character string I am searching for is not present. How to go about this?

row dataframe r
5 Answers

For completeness, since R 3.3.0, grep and friends come with an invert argument:

new_d <- d[grep("K", d$z, invert = TRUE), ]
user_16649780

If you don't want to use ! or invert = TRUE you can also use a REGEX only:

d[ grep('^((?!K).)*$', d$z, perl = TRUE), ]

Taken from here.

user_47428890
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