Order data frame rows according to vector with spe

Question

Is there an easier way to ensure that a data frame's rows are ordered according to a "target" vector as the one I implemented in the short example below?

df <- data.frame(name = letters[1:4], value = c(rep(TRUE, 2), rep(FALSE, 2)))

df
#   name value
# 1    a  TRUE
# 2    b  TRUE
# 3    c FALSE
# 4    d FALSE

target <- c("b", "c", "a", "d")

This somehow seems to be a bit too "complicated" to get the job done:

idx <- sapply(target, function(x) {
    which(df$name == x)
})
df <- df[idx,]
rownames(df) <- NULL

df 
#   name value
# 1    b  TRUE
# 2    c FALSE
# 3    a  TRUE
# 4    d FALSE

Answer 1

I prefer to use ***_join in dplyr whenever I need to match data. One possible try for this

left_join(data.frame(name=target),df,by="name")

Note that the input for ***_join require tbls or data.frame

Answer 2

Try match:

df <- data.frame(name=letters[1:4], value=c(rep(TRUE, 2), rep(FALSE, 2)))
target <- c("b", "c", "a", "d")
df[match(target, df$name),]

  name value
2    b  TRUE
3    c FALSE
1    a  TRUE
4    d FALSE

It will work as long as your target contains exactly the same elements as df$name, and neither contain duplicate values.

From ?match:

match returns a vector of the positions of (first) matches of its first argument 
in its second.

Therefore match finds the row numbers that matches target's elements, and then we return df in that order.

Answer 3

This method is a bit different, it provided me with a bit more flexibility than the previous answer. By making it into an ordered factor, you can use it nicely in arrange and such. I used reorder.factor from the gdata package.

df <- data.frame(name=letters[1:4], value=c(rep(TRUE, 2), rep(FALSE, 2)))
target <- c("b", "c", "a", "d")

require(gdata)
df$name <- reorder.factor(df$name, new.order=target)

Next, use the fact that it is now ordered:

require(dplyr)
df %>%
  arrange(name)
    name value
1    b  TRUE
2    c FALSE
3    a  TRUE
4    d FALSE

If you want to go back to the original (alphabetic) ordering, just use as.character() to get it back to the original state.