unique() {base}

unique() function is a generic function that extracts unique values from a vector, array or data frame.

The parameters of the function are: x: vector, array or data frame to remove duplicated values fromLast:logical indicating if duplication should be considered from the last

#`unique()` function using vectors:
x <- c(10 + 0:5, 1:5, 8:1)
x

##  [1] 10 11 12 13 14 15  1  2  3  4  5  8  7  6  5  4  3  2  1

u1 <- unique(x)
u1

##  [1] 10 11 12 13 14 15  1  2  3  4  5  8  7  6

u2 <- unique(x,  fromLast = TRUE) # different order
u2

##  [1] 10 11 12 13 14 15  8  7  6  5  4  3  2  1

y <- c(5:1,8:1, 10, 1:3)
y

##  [1]  5  4  3  2  1  8  7  6  5  4  3  2  1 10  1  2  3

u3 <- unique(y)
u3

## [1]  5  4  3  2  1  8  7  6 10

u4 <- unique(y,  fromLast = TRUE) # different order
u4

## [1]  8  7  6  5  4 10  1  2  3

#`unique()` function with data frames:
dim(ChickWeight)

## [1] 578   4

head(ChickWeight)

##   weight Time Chick Diet
## 1     42    0     1    1
## 2     51    2     1    1
## 3     59    4     1    1
## 4     64    6     1    1
## 5     76    8     1    1
## 6     93   10     1    1

nrow(unique(ChickWeight))

## [1] 578

unique(ChickWeight$Diet)

## [1] 1 2 3 4
## Levels: 1 2 3 4

length(unique(ChickWeight$weight))

## [1] 212