Edit multiple JSON files in R and saving them to CSV (Alternative for "for" loop) - json

Question

I have multiple JSON files containing Tweets from Twitter. I want to import and edit them in R one by one.
For a single file my code looks like this:
data <- fromJSON("filename.json")
data <- data[c(1:3,13,14)]
data$lang <- ifelse(data$lang!="de",NA,data$lang)
data <- na.omit(data)
write_as_csv(data,"filename.csv")
Now I want to apply this code to multiple files. I found a "for" loop code here:
Loop in R to read many files
Applied to my problem it should look something like this:
setwd("~/Documents/Elections")
ldf <- list()
listjson <- dir(pattern = "*.json")
for (k in 1:length(listjson)){
data[k] <- fromJSON(listjson[k])
data[k] <- data[k][c(1:3,13,14)]
data[k]$lang <- ifelse(data[k]$lang!="de",NA,data[k]$lang)
data[k] <- na.omit(data[k])
filename <- paste(k, ".csv")
write_as_csv(listjson[k],filename)
}
But the first line in the loop already doesn't work.
> data[k] <- fromJSON(listjson[k])
Warning message:
In `[<-.data.frame`(`*tmp*`, k, value = list(createdAt = c(1505935036000, :
provided 35 variables to replace 1 variables
I can't figure out why. Also, I wonder if there is a nicer way to realize this problem without using a for loop. I read about the apply family, I just don't know how to apply it to my problem. Thanks in advance!
This is an example how my data looks:
https://drive.google.com/file/d/19cRS6p_mHbO6XXprfvc6NPZWuf_zG7jr/view?usp=sharing

Answer 1

It should work like this:
setwd("~/Documents/Elections")
listjson <- dir(pattern = "*.json")
for (k in 1:length(listjson)){
# Load the JSON that correspond to the k element in your list of files
data <- fromJSON(listjson[k])
# Select relevant columns from the dataframe
data <- data[,c(1:3,13,14)]
# Manipulate data
data$lang <- ifelse(data$lang!="de",NA,data$lang)
data <- na.omit(data)
filename <- paste(listjson[k], ".csv")
write_as_csv(data,filename)
}
For the second part of the question, apply applies a function over rows or columns of a dataframe. This is not your case, as you are looping through a vector of character to get filenames to be used somewhere else.