R - Dataframe - Replace characters in a string using two columns containing lists of positions and characters

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First time poster, so please let me know how to improve my question if needed. Certainly eager to improve.

I have a data frame that has a column of strings that I need to replace characters in using a column containing a list of multiple positions and another column with a list of characters for those positions. Using example data:

#create the values to build the data frame for use case
food <-"pasta"
string <-"bacorogi"
pos <- c(1,4,7)
chars <- c("m","a","n")

#convert vectors to lists
poslist <-list(pos)
charlist <-list(chars)

#create data frame
df <-data.frame(cbind(food,
           poslist,
           charlist,
           string))

I figured out how to do this when the string, positions, and characters exist as separate vectors using:

for(i in seq_along(pos)) substring(string, pos[i], pos[i]) <- chars[i]
string
[1] "macaroni"

When I try to apply this to the data frame I run into an error:

for(i in seq_along(df$pos)) substring(df$string, df$pos[i], df$pos[i]) <- df$chars[i]

Error in `substring<-`(`*tmp*`, df$pos[i], df$pos[i], value = df$chars[i]) : 
  (list) object cannot be coerced to type 'integer'

To try to properly apply this to a data frame, I tried below and got an error:

 for(i in seq_len(nrow(df))) substring(df$string, df$poslist[i], df$poslist[i]) <- df$charlist[i]

Error in `substring<-`(`*tmp*`, df$poslist[i], df$poslist[i], value = df$charlist[i]) : 
  (list) object cannot be coerced to type 'integer'

I am not really sure how to get around this problem or how to adapt this to a data frame.

I do have more rows in my data frame, but I figured if someone could help me figure out how to do this to one row, I could take it from there. Thanks for any input you can provide!

dataframe r replace string
1 Answers

The nesting is one level deep. So, extract that element and loop

for(i in seq_along(df$pos[[1]])) {
  substring(df$string[[1]], df$pos[[1]][i], 
        df$pos[[1]][i]) <- df$charlist[[1]][i]
 }

-output

df$string
#$string
#[1] "macaroni"

If there are more rows, do a nested loop

for(i in seq_along(df$pos)) {
   for(j in seq_along(df$pos[[i]])) {
      substring(df$string[[i]], df$pos[[i]][j], 
        df$pos[[i]][j]) <- df$charlist[[i]][j]
   }
 }


df$string
#$string
#[1] "macaroni"
user_37322710
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