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(iris)

## [1] 150   5

nrow(unique(iris))

## [1] 149

unique(iris$Sepal.Width)

##  [1] 3.5 3.0 3.2 3.1 3.6 3.9 3.4 2.9 3.7 4.0 4.4 3.8 3.3 4.1 4.2 2.3 2.8
## [18] 2.4 2.7 2.0 2.2 2.5 2.6

length(unique(iris$Sepal.Width))

## [1] 23

par(mfrow = c(1,2))
plot(iris$Sepal.Length, col = 'darkturquoise',type = 'b', frame.plot = F)
plot(unique(iris$Sepal.Length), col = 'darkviolet',type='b', frame.plot = F)