Substituting each row of col1 into the corresponding token in col2 using the apply family

Question

I feel like this has to be a super basic thing to solve but my searching skills are failing me.

df <- data.frame(col1 = c("abc", "def", "ghi"),
                 col2 = c("foo ~xyz~", "~xyz~ bar", "blah ~xyz~ blah"))
col1   col2
abc    foo ~xyz~
def    ~xyz~ bar
ghi    blah ~xyz~ blah

I want to gsub() each row of col1 into the corresponding ~xyz~ token in col2 . The desired output is:

col1   col2
abc    foo abc   
def    def bar
ghi    blah ghi blah

I can solve this using a for loop but I feel like there's got to be a way to do this with vapply or sapply .

My for loop solution is as follows:

for (i in 1:nrow(df)) {
     itemhold <- df$col1[i]
     df$col2[i] <- gsub("~xyz~", itemhold, df$col2[i])
}

Any tips would be greatly appreciated. If it's not painfully obvious by now, I'm fairly new to R and it's my first language.

Edit: I deleted some stuff about a function I used for these purposes because as I actually worked through my minrep example I realized it wasn't needed--I use the function in a special case that isn't really relevant here.

Answer 1

You can do this with stringr without any looping or apply ing:

df <- data.frame(col1 = c("abc", "def", "ghi"),
                 col2 = c("foo ~xyz~", "~xyz~ bar", "blah ~xyz~ blah"),
                 stringsAsFactors = FALSE)

df$col2_replaced = str_replace(df$col2, "~xyz~", df$col1)

Output:

> df
  col1            col2 col2_replaced
1  abc       foo ~xyz~       foo abc
2  def       ~xyz~ bar       def bar
3  ghi blah ~xyz~ blah blah ghi blah

Answer 2

You can do this with apply like so:

df$col2 <- apply(df, 1, 
             function(row) gsub(pattern="~xyz~", replacement=row["col1"], x=row["col2"]))
#   col1          col2
# 1  abc       foo abc
# 2  def       def bar
# 3  ghi blah ghi blah

Here it is with mapply (aka "multivariate apply") instead:

df$col2 <- mapply(
             function(rep, string) gsub(pattern="~xyz~", replacement=rep, x=string),
             df$col1, df$col2)
#   col1          col2
# 1  abc       foo abc
# 2  def       def bar
# 3  ghi blah ghi blah