! grep in R - finding items that do not match [duplicate]

Question

I want to find rows in a dataframe that do not match a pattern.

 Key = c(1,2,3,4,5)
 Code = c("X348","I605","B777","I609","F123")
 df1 <- data.frame(Key, Code)

I can find items beginning with I60 using:

 df2 <- subset (df1, grepl("^I60", df1$Code))

But I want to be able to find all the other rows (that is, those NOT beginning with I60). The invert argument does not work with grepl. grep on its own does not find all rows, nor can it pass the results to the subset command. Grateful for help.

Answer 1

You could use the [ operator and do

df1[!grepl("I60", Code),]

(Suggested clarification from @Hugh:) Another way would be

df1[!grepl("I60",df1$Code),]

Here is the reference manual on array indexing, which is done with [:

http://cran.r-project.org/doc/manuals/R-intro.html#Array-indexing

Answer 2

Also, you can try this:

 Key = c(1,2,3,4,5)
Code = c("X348","I605","B777","I609","F123")
df1 <- data.frame(Key, Code)
toRemove<-grep("^I60", df1$Code)
df2 <- df1[-toRemove,]