Other basic functions

sort()

This function sorts(orders) a vector in ascending or descending order.

# sort(vector, decreasing=F) sorts a vector from smallest to largest
sort(data$score1)     # returns a sorted version of 'score1' variable (vector)

##  [1] 14 17 23 23 25 27 27 31 31 32 32 33 34 35 35 36 39 40 45 51

# To sort the vector from largest to smallest, include 'decreasing=T'
sort(data$score1, decreasing = T)

##  [1] 51 45 40 39 36 35 35 34 33 32 32 31 31 27 27 25 23 23 17 14

Note that ‘score1’ variable in ‘data’ object remains unsorted as we did not assign the sorted vector.

data$score1

##  [1] 35 23 14 17 23 35 27 33 32 31 34 27 51 36 39 45 31 40 25 32

rank()

This function returns a vector of the ranks of the values in a vector.

# rank(vector) 
# For example, the lowest value would have a rank of 1 and the second-lowest value would have a rank of 2
rank(data$score1)    # returns the ranks of the values of 'score1' variable

##  [1] 14.5  3.5  1.0  2.0  3.5 14.5  6.5 12.0 10.5  8.5 13.0  6.5 20.0 16.0 17.0
## [16] 19.0  8.5 18.0  5.0 10.5

# Note that the default option for dealing with ties is to use the 'average' value

order()

This function returns the sorting index (an integer vector containing the permutation to sort a vector into ascending or descending order)

# order(vector, decreasing=F) 
order(data$score1)   # returns index to sort 'score1' variable in 'ascending' order 

##  [1]  3  4  2  5 19  7 12 10 17  9 20  8 11  1  6 14 15 18 16 13

# To get an index to sort 'score1' variable in 'descending' order:
order(data$score1, decreasing = T)

##  [1] 13 16 18 15 14  1  6 11  8  9 20 10 17  7 12 19  2  5  4  3

Using [ ] and order() functions together, we can reorder data.

# vector[order(vector)] arranges a vector in ascending or descending order
score1 <- data$score1   # a vector
reorder.sc1 <- score1[order(score1, decreasing=T)]  # reorder 'score1' vector from largest to smallest
reorder.sc1

##  [1] 51 45 40 39 36 35 35 34 33 32 32 31 31 27 27 25 23 23 17 14

# This is actually equivalent to :
sort(data$score1, decreasing=T)     # sort/order a vector from largest to smallest  

##  [1] 51 45 40 39 36 35 35 34 33 32 32 31 31 27 27 25 23 23 17 14

In a similar way, we can rearrange a dataframe (or matrix) by a specific variable in its ascending or descending order.

# data[order(vector), ] reorders 'rows' by 'vector' in ascending or descending order
data.new <- data[order(data$score1, decreasing=T), ] # reorder 'data' by 'score1' in descending order
data.new

##    ID group score1 score2
## 13 13     2     51     45
## 16 16     2     45     41
## 18 18     2     40     17
## 15 15     2     39     37
## 14 14     2     36     26
## 1   1     1     35     45
## 6   6     1     35     47
## 11 11     2     34     48
## 8   8     1     33     50
## 9   9     1     32     15
## 20 20     2     32     27
## 10 10     1     31     37
## 17 17     2     31     25
## 7   7     1     27     37
## 12 12     2     27     16
## 19 19     2     25     15
## 2   2     1     23     14
## 5   5     1     23     27
## 4   4     1     17     25
## 3   3     1     14     26