Data.Table with Two String Columns of Set Elements, Extract Unique Rows with Each Row Unsorted

R data.table duplicate rows with a pair of columns

The linked answer ( is nearly a duplicate, and so is , but here goes again, with a slight twist:


# Gene1 Gene2 Ens.ID.1 Ens.ID.2 CORR
#1: FOXA1 MYC ENSG000000129.13. ENSG000000129.11 0.9953311
#2: EGFR CD4 ENSG000000129 ENSG000000129.12 0.9947215

If you have >2 or many keys to dedup by, you are probably best off converting to a long file, sorting, back to a wide file and then de-duplicating. Like so:

dupvars <- c("Gene1","Gene2")
sel <- !duplicated(
melt(dt[, c(.SD,id=.(.I)), .SDcols=dupvars], id.vars="id")[
order(id,value), grp := seq_len(.N), by=id],
id ~ grp

Keep first row by multiple columns in an R data.table

data.table provides S3 methods for unique, duplicated and anyDuplicated

unique(dt, by = c('x','y'))

will give you what you want.

Extracting unique rows from a data table in R

Before data.table v1.9.8, the default behavior of method was to use the keys in order to determine the columns by which the unique combinations should be returned. If the key was NULL (the default), one would get the original data set back (as in OPs situation).

As of data.table 1.9.8+, method uses all columns by default which is consistent with the in base R. To have it use the key columns, explicitly pass by = key(DT) into unique (replacing DT in the call to key with the name of the data.table).

Hence, old behavior would be something like

library(data.table) v1.9.7-
a <-, 120, replace = TRUE), ncol = 3))
b <- data.table(a, key = names(a))
## key(b)
## [1] "V1" "V2" "V3"
## [1] 8 3

While for data.table v1.9.8+, just

b <- data.table(a) 
## [1] 8 3
## or dim(unique(b, by = key(b)) # in case you have keys you want to use them

Or without a copy

## [1] 8 3

Removing duplicate rows from data frame in R

We can use data.table. Convert the 'data.frame' to 'data.table' (setDT(df1)), grouped by the pmin(A, B) and pmax(A,B), if the number of rows is greater than 1, we get the first row or else return the rows.

setDT(df1)[, if(.N >1) head(.SD, 1) else .SD ,.(A=pmin(A, B), B= pmax(A, B))]
# A B prob
#1: 1 2 0.1
#2: 1 3 0.2
#3: 1 4 0.3
#4: 2 3 0.1
#5: 2 4 0.4

Or we can just used duplicated on the pmax, pmin output to return a logical index and subset the data based on that.

 setDT(df1)[!duplicated(cbind(pmax(A, B), pmin(A, B)))]
# A B prob
#1: 1 2 0.1
#2: 1 3 0.2
#3: 1 4 0.3
#4: 2 3 0.1
#5: 2 4 0.4

Unique rows, considering two columns, in R, without order

There are lot's of ways to do this, here is one:

unique(t(apply(df, 1, sort)))
duplicated(t(apply(df, 1, sort)))

One gives the unique rows, the other gives the mask.

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