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rlistnested-loopsconcatenation

Create a list concatenating a list element and character string in R

I am trying to create a list of requests called requests. I have a list of hundreds of products, but I simplify for this example code. 

products <- list()
products[[1]] <- c("77295T", "67619Q", "9528QR")
products[[2]] <- c("B7295T", "676193")
requests <- vector("list",length(products[[1]]))
length(requests)
i <- 1
for (i in 1:(length(products[[1]])))  {
    requests[[i]] <- cat('"',noquote(products[[1]][[i]]),'~XPORT"', sep = '')  
   }

results in:

"77295T~XPORT""67619Q~XPORT""9528QR~XPORT"

The end result I am looking for is a request list of length 3 with the following three elements:

requests[[1]] 
"77295T~XPORT"

requests[[2]]
"67619Q~XPORT"

requests[[3]]
"9528QR~XPORT"

Background: Eventually I want requests to be a nested list (a list of lists); in my dataset products is a list, so that is why I provide products[[2]], even though my question relates to just iterating over products[[1]]. Replacingproducts[[1]]` with an equivalent products1 also creates the same output. That code is here:

products1 <- c("77295T", "67619Q", "9528QR")
i <- 1
for (i in 1:(length(products1))) {
  requests[[i]] <- cat('"',noquote(products1[[i]]),'~XPORT"', sep = '')  
  }

This more simple code provides the same results:

"77295T~XPORT""67619Q~XPORT""9528QR~XPORT"

I do realize that the for loop I called may not be necessary. I am trying to gradually learn how to "vectorize" my R code. Any suggestion for further vector-elegance in this code would be appreciated.

Solution

  • I guess what you are looking for is this:

    requests <- lapply(products[[1]], function(x){paste0(x, "~XPORT")})
requests
# [[1]]
# [1] "77295T~XPORT"
#
# [[2]]
# [1] "67619Q~XPORT"
#
# [[3]]
# [1] "9528QR~XPORT"

    And if you wish to do this to all vectors in products, I would use a loop:

    request <- list()
for(i in 1:length(products)){
   request[[i]] <- lapply(products[[i]], function(x){paste0(x, "~XPORT")})
}

    I'm sure this is just one of many ways to accomplish this.

    Edit

    An alternative to the above without any loops, would be to use sapply instead of for

    sapply(products, function(y){
  lapply(y, function(x) paste0(x, "~XPORT"))
})