using loop variable in text string for loops in R

Question

If i have multiple csv files stored as: m1.csv, m2.csv,.....,m50.csv and what I would like to do is load each csv into R, run the data in the i-th file and store it as a variable: m'i'. I am trying to use a for loop but i'm not sure if i can quite use them in such a way. For example:

for (i in 1:100){
     A<-as.matrix(read.csv("c:/Users/Desktop/m"i".csv))
     ...
     #some analysis on A
     ...
     m"i"<- #result of analysis on A
     }
     V<-cbind(m1,m2, .... ,m100)

You'll need to use paste0 to assemble paths and names, and probably assign instead of <-, as your name will be quoted, but yes, the approach is pretty common. You won't want to do analysis in the loop, though; save that for later. You may also want to save them into a list—instead of the global environment—to make looping over them later easier. It also simplifies naming. — alistaire
– alistaire, Commented Mar 16, 2016 at 6:31
@alistaire While I can agree that OP's approach is pretty common, I don't think it can be considered "correct" and it shouldn't be encouraged. The use of assign is almost never a good idea. A simple lapply would solve OP's task in a cleaner way. — nicola
– nicola, Commented Mar 16, 2016 at 6:36

Sunny Sunny · Accepted Answer · 2016-03-16 06:33:44Z

1

Try this

filenames = list.files(getwd())
filenames = filenames[grepl(".csv",file_names)]
files = lapply(filenames, read.csv)
files = do.call(rbind,files)

answered Mar 16, 2016 at 6:33

Sunny Sunny

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7 Comments

nicola Over a year ago

The idea is good, but there are some inaccuracies. 1) No need to call list.files, since in the OP the file names are specified: filenames<-paste0("c:/Users/Desktop/m",1:100,".csv") should be the way. 2) The analysis part is missing: OP should define a function (let's call it makeAnalysis) that does the task. 3) At the end, OP wants to cbind rather than rbind. A simple line should be do.call(cbind,lapply(filenames, function(x) makeAnalysis(read.csv(x)))).

WeakLearner Over a year ago

@nicola I've written up a function as you recommended, im just wodnering if i want to add the parameter row.names=1 to read.csv where should i do that? it seems to give me an error if i put it in the do.call

WeakLearner Over a year ago

@nicola further, as my function involves matrix calculations, i get the non-conformable arguments error, not quite sure how to deal with this

nicola Over a year ago

@dimebucker91 Arguments of read.csv should go into the read.csv call. For instance, in my line you should replace read.csv(x) with read.csv(x,row.names=1). For the second issue, I suspect that it's a bug of your function and cannot tell for sure to what it is due. It seems that you are trying to make a matrix product between matrices with wrong numbers of row or cols.

nicola Over a year ago

@dimebucker91 Please, check what you wrote. Once it's row.names and the other rownames. The error message was clear, you should have solved it by yourself.

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