Question: I have a dataset in R which looks like this:

```
    x1 x2  x3
1:  A Away  2
2:  A Home  2
3:  B Away  2
4:  B Away  1
5:  B Home  2
6:  B Home  1
7:  C Away  1
8:  C Home  1

```

Based on the values in columns x1 and x2, I want to remove the duplicate rows. I have tried the following:

```
df[!duplicated(df[,c('x1', 'x2')]),]

```

It should remove rows 4 and 6. But unfortunately it is not working, as it returns exactly the same data, with the duplicates still present in the dataset. What do I have to use in order to remove rows 4 and 6?

Answer: 
I'd just do:

```
unique(df, by=c("x1", "x2")) # where df is a data.table

```

This'd have been quite obvious if you'd just looked at `?unique`.

PS: given the syntax in your Q, I wonder if you are aware of the basic differences between data.table and data.frame's syntax. I suggest you read the [vignettes](https://github.com/Rdatatable/data.table/wiki/Getting-started) first.
```
library("data.table")
setDT(df)[, .SD[1], by = .(x1, x2)]

#     x1   x2 x3
# 1:  A Away  2
# 2:  A Home  2
# 3:  B Away  2
# 4:  B Home  2
# 5:  C Away  1
# 6:  C Home  1

```