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

Solution 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

Solution 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).

Solution 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.

Solution 4

You can also use the sqldf package in R.

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

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Comments

[AnilGoyal]

This won't give output as expected by OP!!

[Alvaro Morales]

is there a function that replaces "pull" and "unique" altogether?

[Vishal Kumar Sahu]

Currently I have not got such short notation in R. Python might be having it.