List distinct values in a vector in R

Question

How can I list the distinct values in a vector where the values are replicative? I mean, similarly to the following SQL statement:

SELECT DISTINCT product_code
FROM data

Answer 1

Do you mean unique:

R> x = c(1,1,2,3,4,4,4)
R> x
[1] 1 1 2 3 4 4 4
R> unique(x)
[1] 1 2 3 4

Answer 2

If the data is actually a factor then you can use the levels() function, e.g.

levels( data$product_code )

If it's not a factor, but it should be, you can convert it to factor first by using the factor() function, e.g.

levels( factor( data$product_code ) )

Another option, as mentioned above, is the unique() function:

unique( data$product_code )

The main difference between the two (when applied to a factor) is that levels will return a character vector in the order of levels, including any levels that are coded but do not occur. unique will return a factor in the order the values first appear, with any non-occurring levels omitted (though still included in levels of the returned factor).

Answer 3

Try using the duplicated function in combination with the negation operator "!".

Example:

wdups <- rep(1:5,5)
wodups <- wdups[which(!duplicated(wdups))]

Hope that helps.

Answer 4

You can also use the sqldf package in R.

Z <- sqldf('SELECT DISTINCT tablename.columnname FROM tablename ')

Answer 5

another way would be to use dplyr package:

x = c(1,1,2,3,4,4,4)
dplyr::distinct(as.data.frame(x))

Answer 6

In R Language (version 3.0+) You can apply filter to get unique out of a list-

data.list <- data.list %>% unique

or couple it with other operation as well

data.list.rollnumbers <- data.list %>% pull(RollNumber) %>% unique

unique doesn't require dplyr.