CODEWITHSUNDEEP
r
systemdebt
systemdebt

Reputation: 4951

how to use lapply in R

I am trying to use lapply so that I can apply a custom function on all elements of a vector in R. I am trying to avoid using for loop here .

This is what I have so far:

writeToHDFS <- function(fileName){
  print(fileName)
  hdfs.init()
 modelfile <- hdfs.file(fileName, "w")
  hdfs.write(gaDataUser, modelfile)
 hdfs.close(modelfile)
}

fileNames <- c("gaDataUser", "gaDataSession", "gaDataSources","gaDataEventTracking", "gaDataEcommerce", "gaDataEcommerce2", "gaDataEcommerce3", "gaDataEcommerce4")


lapply(fileNames,writeToHDFS(x))

I have variables with the names mentioned in the character vector fileNames.

What I need to know:

  1. How to pass each string from the vector fileNames to function writeToHDFS since I would like this function to be executed for every element in the vector.

  2. How to use string name to access variables of that name in the function. For example:

At this line,I have to access variable with name same as string passed to fileName variable in the function.

hdfs.write(variableWithData, modelfile)

3. Can I pass the variable fileName to 

modelfile <- hdfs.file(fileName, "w")

instead of passing a string for file name ?

Upvotes: 0

Views: 3808

Answers (2)

Zheyuan Li
Zheyuan Li

Reputation: 73395

I am trying to use lapply so that I can apply a custom function on all elements of a vector in R

In this situation, you should use tapply:

tapply(fileNames, 1:length(fileNames), writeToHDFS)

lapply, is short for "list-apply", but fileNames is a vector not a list.

Since you are already pretty well-aimed at using lapply, you can learn from ?lapply.

Upvotes: 2

jjaskulowski
jjaskulowski

Reputation: 2574

writeToHDFS(x) gives you return value of function. But you want to pass function so:

lapply(fileNames,writeToHDFS)

Upvotes: 1

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