CODEWITHSUNDEEP
rlistdata.table
Phann
Phann

Reputation: 1327

Output of data.table aggregation as list

How can I group a data.table e.g. with filenames by metadata and store each group in a list-item?

Input:

DT <- data.table(files = 1:10, meta = c(rep(1, 6), rep(2,4)))

I thought of something like:

MyList <- DT[, files, by = meta] #something like that

Desired Output:

[[1]]
[1] 1 2 3 4 5 6

[[2]]
[1] 7 8 9 10

The above example is simplified in the case that meta are actually more columns (to group by) and some rows are selected before. Is there a simple way to go (preferable a data.table-solution), or do I have to use some other way like

lapply(unique(DT$meta), function(x) DT[meta == x]$files)

?

Upvotes: 0

Views: 34

Answers (1)

akrun
akrun

Reputation: 887391

We can wrap it in a list

DT1 <- DT[, .(files = list(files)), meta]
DT1$files
#[[1]]
#[1] 1 2 3 4 5 6

#[[2]]
#[1]  7  8  9 10

Upvotes: 1

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