merge() failed in the lapply loop

[Limin_Chen]

I have the following script is working but failed to generate the output I expected.
I have three csv files for the lapply to loop, and it is able to generate the df dataframe. But I want to combine all 3 df from each csv file into one dataframe, that is why I use merge(). But the merge() doesn't work. Can anyone help me diagnose where I went wrong with my code?

Thanks in advance.

To reproduce my issue, you just need to create a ./test/ folder locally. Then the following code will generate 3 random csv files, and run the lapply.

# generate randome csv files
for (i in 1:3){
d1 <- data.frame(replicate(3, sample(0:2,4,rep=TRUE)))
colnames(d1) <- c("a", "b", "c")
path1 <- paste0( "./test/t",i,"1.csv")
write.csv(d1,path1, row.names = TRUE)
}

files <- list.files(path = "./test", pattern = ".csv", full.names = TRUE, recursive = FALSE)

X<- c(1,2,3,4)
df0 <- data.frame(X)

lapply(files, function(x){
  df <- read.csv(x, header = TRUE)
  df0 <- merge(df0,df, by = "X")
}
)

[williaml]

Can you provide a reproducible example?

FAQ: How to do a minimal reproducible example ( reprex ) for beginners

A minimal reproducible example consists of the following items: A minimal dataset, necessary to reproduce the issue The minimal runnable code necessary to reproduce the issue, which can be run on the given dataset, and including the necessary information on the used packages. Let's quickly go over each one of these with examples: Minimal Dataset (Sample Data) You need to provide a data frame that is small enough to be (reasonably) pasted on a post, but big enough to reproduce your issue. Let's say, as an example, that you are working with the iris data frame head(iris) #> Sepal.Length Sepal.Width Petal.Length Petal.Width Species #> 1 5.1 3.5 1.4 0.…

[Limin_Chen]

Hi Williaml,

I just rewrote my code to reproduce the issue. You just need to create a 'test' folder locally, then you can copy and paste my previous code in r. You will see the merge() doesn't work. I also tested by set i =0 in the beginning, and put i = i+ 1 in the middle to see if lapply() will add 1 each time finish the loop. And it didn't work.

For now I used for loop again to make it work.

If you can explain the difference between lapply and for loop. That will be great.

Thanks a lot.

Best,