I am trying to create a df where I add a character into a string at a position defined by another column- but I only want the code to count letters and not numbers or other characters while it does this, hopefully the example tables make this clearer

my initial data looks like this.

i use the following code

library(stringi)
stri_sub(df$String,df$Insert_pos 1, df$insert_pos-1) <- "[ 20]"

and it only half works--- I only want it to count the Letters and not the numbers already added when it adds the new characters. as shown below

I think the way to do it would be to specify to only count letters, but I cant find how to specify this in Stringi/ not sure if it is possible.

Any help would be great,

Thanks!

CodePudding user response：

You can change the value of your df$Insert_pos column for the next possible position:

df <- data.frame(
  String = c("PEPTIDE", "PE[ 10]TIDE"),
  Insert_pos = c(3,3)
)

df$Insert_pos <- ifelse(
  stri_sub(df$String,df$Insert_pos, df$Insert_pos) %in% c("[", "]", " ", 1:9), 
  df$Insert_pos   5 , 
  df$Insert_pos)

library(stringi)
stri_sub(df$String,df$Insert_pos 1, df$Insert_pos-1) <- "[ 20]"

df

This gives you then:

            String Insert_pos
1     PEP[ 20]TIDE          3
2 PE[ 10]T[ 20]IDE          8

CodePudding user response：

You can use sub:

sub("(([[:alpha:]][^[:alpha:]]*){3})", "\\1[ 20]", df$String)
#[1] "PEP[ 20]TIDE"     "PE[ 10]T[ 20]IDE"

In this case using only upper case will also work.

sub("(([A-Z][^A-Z]*){3})", "\\1[ 20]", df$String)

sub("(([[:upper:]][^[:upper:]]*){3})", "\\1[ 20]", df$String)