Sorting of Arrays in R Programming

Prerequisite: R – Array

A vector is a uni-dimensional array, which is specified by a single dimension, length. A Vector can be created using the ‘c()‘ function. A list of values is passed to the c() function to create a vector. Sorting can be done either in ascending order or descending. There are few things which should be kept in mind before sorting. They are as follows:

• Order in which sorting needs to be performed – Ascending/Descending.
• Sorting according to multiple column criteria.
• Handling missing and duplicate values during sorting. The analyst must decide what should be done with missing and duplicate values. The overall impact on the data should be considered before removing or replacing null values.

Method 1: sort() function

sort() function in R is used to sort a vector. By default, it sorts a vector in increasing order. To sort in descending order, add a “decreasing” parameter to the sort function.

Syntax:

sort(name_of_vector, decreasing = TRUE)

Parameters:

name_of_vector: Vector to be sorted

decreasing: Boolean value to sort in descending order

Example 1:

Output:

[1] 1 2 3 4 5 6 7 8 9

Example 2:

Output:

[1] 9 8 7 6 5 4 3 2 1

Note: The major drawback of the sort() function is that it cannot sort data frames.

Method 2: order() function

To overcome the drawback in method 1, we use the order() function, which also sorts data frames according to the specified column. To sort in decreasing order add negative sign. Data can also be sorted with multiple criteria. Suppose if the age of two persons is the same then, we can sort them on the basis of their names i.e. lexicographically. See the below examples.

Example 1:

Output:

   Age  Name
4  5    Jack
1  12   Johnny
3  15   Alfie
2  21   Glen
5  25   Finch

Example 2:

Output:

[1] 6 5 4 3 2 1

Example 3:

Output:

  Age   Name
6  12   Aaron
4  12   Jack
1  12   Johnny
3  15   Alfie
2  21   Glen
5  25   Finch

Note: The output above is the indices of numbers. For instance, 60 is the largest in vector and had index 6. Thus, 6 is displayed first. 

Method 3: Sorting array using the loop

• Create a linear array, say arr
• Create a variable swap. If swap is false after traversing the entire array, it means the array is already sorted and break the loop
• Else, run loop and copy original array into another array, say newArr, and start comparing adjacent elements in the original array
• If the current element is smaller than the previous element, then copy the current element of arr into the previous position of newArr and the previous element of arr into the current position of newArr. The newArr now has swapped elements.
• Copy newArr to original array arr and make swap = TRUE.
• Repeat until arr is sorted

Below is the implementation of the above approach.

Output:

[1] 1 2 3 4 4 5 5 6 9

Method 4: The use of dplyr package

dplyr package is easy to use and reliable. The package includes arrange() method to sort the data. See the below examples.

Example 1:

Output:

   Age  Name
4  5    Jack
1  12   Johnny
3  15   Alfie
2  21   Glen
5  25   Finch