如何在 R 中循环遍历 mapply？

Question

I am trying to concatenate strings using mapply function in R. However, I want one of the strings to be variable in mapply function. I have a snippet of my code below:

strings<-data.frame(x=c("dsf","sdf","sdf"))
strings2<-data.frame(extension=c(".csv",".json",".xml"))

for (i in 1:3)
{
  strings_concat<-mapply(function(string1,string2) paste0(string1,string2),strings$x,strings2$extension[i])%>%
    data.frame()%>%
    unlist()%>%
    data.frame()

 #dosomething with strings_concat
}

But this is giving me the last iteration only

strings_concat

dsf.xml
sdf.xml
sdf.xml

bust instead, the desired output is as follows:

strings_concat

dsf.csv 
sdf.csv 
sdf.csv 

dsf.json 
sdf.json 
sdf.json 

dsf.xml
sdf.xml
sdf.xml

At every iteration, i want to combine strings_concat with another dataframe and save it. Can anyone help me if there is an easy way to do this in R?

Answer 1

Perhaps, outer is a better option here:

strings_concat <- c(outer(strings$x, strings2$extension, paste0))
strings_concat
#[1] "dsf.csv"  "sdf.csv"  "sdf.csv"  "dsf.json" "sdf.json" "sdf.json" 
#    "dsf.xml"  "sdf.xml"  "sdf.xml" 

You can add it in a data.frame:

df <- data.frame(strings_concat)

---

If you want to add some additional steps at each iteration you can use lapply :

lapply(strings2$extension, function(x) {
  strings_concat <- paste0(strings$x, x)
  #do something with strings_concat
})

Answer 2

All you should need to do is make sure you are continually augmenting your dataset. So I think this should do the trick:

strings<-data.frame(x=c("dsf","sdf","sdf"))
strings2<-data.frame(extension=c(".csv",".json",".xml"))

# We are going to keep adding things to results
results = NULL

for (i in 1:3)
{
  strings_concat<-mapply(function(string1,string2) paste0(string1,string2),strings$x,strings2$extension[i])%>%
    data.frame()%>%
    unlist()%>%
    data.frame()
 # Here is where we keep adding things to results
 results = rbind(results, strings_concat)
}

print(results)

Caution: not in front a computer with R so this code is untested