Moving some rows of a data frame to the end based on a match vector

Try this:

x <- as.character(df$id) %in% matchlist
rbind(df[!x,], df[x,])

       # id  A      B
# 2  match4  4     in
# 8  match9  H  under
# 9  match8  j     in
# 13 match4 19 beside
# 1  match1  6     in
# 3  match1  8     in
# 4  match2  3    out
# 5  match3  T   over
# 6  match2  8     in
# 7  match1  H   over
# 10 match2  3    out
# 11 match1 20  under
# 12 match3  2    out

Consider this short tidyverse solution:

mydata %>%
  arrange(id %in% match_list)

Here is a solution without grep:

matched <- mydata$id %in% matchlist
mydata2 <- rbind(mydata[!matched,], mydata[matched,])

You could of course order the matched rows before the rbind, then you would get exactly the same output as in your example.