R two dimensional array containing dataframe rows

Question

So, I lately started working with R for a research I'm interested in, and I'm trying to create a multi dimensional array that would contain dataframe rows.

I have a large data frame containing many columns, that are either numeric, or strings. For the sake of simplicity, let's work with 3 columns: thread_id: an integer number between 1 and 10100. user_id: an integer number given to users. post_name: a string that gives us the title of the post

I would like to create a datastructure, that's preferably a two dimensional array, where at the first dimension we have the thread_id, and at the second we have a row from the dataframe.

So, as a return to for

DataSet[1][1], I'd get thread_id: 1, user_id: 100, post_name: "some name 1"
DataSet[1][2], I'd get thread_id: 1, user_id: 101, post_name: "some name 2"
DataSet[5][10], I'd get thread_id: 5, user_id: 900, post_name: "some name 3"

Is this possible to do in R? I only have previous experiences with Java, and in that it is possible to solve with an array for Objects.

Thanks for all the help!

Welcome to SO. First of all you should read [here](http://stackoverflow.com/help/how-to-ask) about how to ask a good question; a good question has better changes to be solved and you to receive help. On the other hand a read of [this](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) is also good. It explains how to create a reproducible example in R. Help users to help you by providing a piece of your data a desired output and things you have tried so far. — SabDeM, May 14 '16 at 13:33

score 0 · Answer 1 · answered May 14 '16 at 13:41

0

If, say, thread_id took on values 1 to 5, you could use:

mylist <- list()
for(i in 1:5)
    mylist[[i]] <- myData[thread_id==i,]

You could of course use max(myData$thread_id) instead of 5...

answered May 14 '16 at 13:41

Dominic Comtois

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score 0 · Answer 2 · answered May 14 '16 at 15:03

0

Here is an alternative for you.

Assumption: df is a data.frame

convert.to.str <- function(df){
    df_col <- names(df)
    val <- unlist(df)

    ans <- paste(df_col,val,sep=': ')

    final_ans <- paste(ans,collapse=', ')
}

int_ans <- data.frame(thread_id = df$thread_id, ans = apply(df,1,convert.to.str), nrow2=1:nrow(df))

library(reshape2)

int_ans2 <- dcast(int_ans,thread_id ~ nrow2,value.var='ans')

DataSet <- int_ans2[2:ncol(int_ans2)]

dimnames(DataSet)[[1]] <- int_ans2$thread_id

answered May 14 '16 at 15:03

Kunal Puri

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Hey, thanks for sharing! Seems to have worked perfectly for int_ans, akthough it only populated number 13 at int_ans2 (99 times :D ). Any idea why this might happen? All I did was change the variables to the names I have them in my program. – M. Küsz May 14 '16 at 18:47
@M.Küsz Can you please share the code modified by you? – Kunal Puri May 15 '16 at 03:26
@M.Küsz The code seems to be absolutely all right. Actually, I am not able to recognise the error about which you are talking about. I would be grateful if you could include the glimpse of dataset along with the error that you are getting. – Kunal Puri May 15 '16 at 12:32
@M.Küsz Can you please explain the meaning of this line `it only populated number 13 at int_ans2 (99 times :D)`? Is number 13 coming 99 times in rownames of int_ans2? – Kunal Puri May 16 '16 at 05:13

R two dimensional array containing dataframe rows

2 Answers2