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duplicated() and unique() functions in R


duplicated() function is a general function that determines which elements are duplicated, it returns a logical vector:
The parameters of the function are: 
x: vector, array or data frame
 fromLast:logical indicating if duplication should be considered from the last
x = c(5:1,5:1,5)
x
##  [1] 5 4 3 2 1 5 4 3 2 1 5
duplicated(x)
##  [1] FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
duplicated(x, fromLast = TRUE)
##  [1]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE
## extract duplicated elements, those elements that duplicated(x) == TRUE, may be repeted elements:
x[duplicated(x)]
## [1] 5 4 3 2 1 5
## extract unique elements
x[!duplicated(x)]
## [1] 5 4 3 2 1
## extract unique elements starting from the righmost value (different order):
x[!duplicated(x, fromLast = TRUE)]
## [1] 4 3 2 1 5
#duplicated using a data frmae
duplicated(iris)
##   [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [12] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [23] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [34] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [45] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [56] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [67] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [78] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [89] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [100] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [111] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [122] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [133] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE
## [144] FALSE FALSE FALSE FALSE FALSE FALSE FALSE
duplicated(iris$Sepal.Length)
##   [1] FALSE FALSE FALSE FALSE FALSE FALSE  TRUE  TRUE FALSE  TRUE  TRUE
##  [12] FALSE  TRUE FALSE FALSE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
##  [23]  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE
##  [34] FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE
##  [45]  TRUE  TRUE  TRUE  TRUE FALSE  TRUE FALSE FALSE FALSE  TRUE FALSE
##  [56]  TRUE FALSE  TRUE FALSE  TRUE  TRUE FALSE FALSE FALSE FALSE FALSE
##  [67]  TRUE  TRUE FALSE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE
##  [78]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
##  [89]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
## [100]  TRUE  TRUE  TRUE FALSE  TRUE  TRUE FALSE  TRUE FALSE  TRUE FALSE
## [111]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE  TRUE  TRUE  TRUE
## [122]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE FALSE FALSE
## [133]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE
## [144]  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE  TRUE

anyDuplicated() function returns the position of the first element duplicated:
x = c(9:1, 20, 10:6,21,10)
x
##  [1]  9  8  7  6  5  4  3  2  1 20 10  9  8  7  6 21 10
duplicated(x)
##  [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [12]  TRUE  TRUE  TRUE  TRUE FALSE  TRUE
anyDuplicated(x)  #first element found to be duplicated
## [1] 12
anyDuplicated(x, fromLast = TRUE) #first element found to be duplicated
## [1] 11
duplicated(iris)
##   [1] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [12] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [23] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [34] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [45] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [56] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [67] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [78] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
##  [89] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [100] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [111] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [122] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE
## [133] FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE FALSE  TRUE
## [144] FALSE FALSE FALSE FALSE FALSE FALSE FALSE
anyDuplicated(iris) ## 143
## [1] 143

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
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