As we know there are three List of Loops
- While Loop ( I have posted on this in my previous post, please refer this below link if not explored)
2.For Loop: we will be discussing in this Post
3.Repeat Loop : we will discuss on this in next Post
There are two Loop control statements:
1.Break statement
2. Next statement
Before we dive into the examples, let’s start with a quick theoretical introduction to for-loops…
The for loop in R is very valuable when we need to iterate over a list of elements (vectors, Matrix, List & data frame) or a range of numbers.
It is an entry-controlled loop, in this loop the test condition is tested first, then the body of the loop is executed, the loop body would not be executed if the test condition is false.
For Loop starts with keyword For and Just Like while Loop, it also has a Simple braces and then Curly braces, The curly Braces are indeed for the body of the loop and the Open Braces doesn’t specify the Condition/Expression, Instead it specifies the iterations of the loop.
In the following, I’ll show you 7 examples for the application of for-loops in R. So keep on reading!
Now don’t get afraid, don’t get worried
we won’t be digging too much into vectors, Lists, Matrix in this specific tutorial but this is our first encounter of the elements and it’s natural because R is all about vectors and vector as operations, matrix and Lists we’ll drill into those topics in a lot and in detail in the next posts, but for now let me show you a quick intro or show you how we’re using those elements in For Loop.
1.For Loop Through Vector in R (Basics) :
Syntax Written in Source Pane:
# 1. working on For Loop Through Vectors
# Head of for Loop
for (i in 1 : 10) {
#code Block
val1 <- i ** 2
#Prints the val1 variable value in console
print(val1 )
}
In the above R code, we are specifying within the head of the for-loop that we want to run through a vector containing ten elements from the first element (i.e. 1) to the last element (i.e. 10).
Within the body of the for-loop we are then creating an output called var1, which contains the I value from the for Loop (1 to 10) to the power of 2. We are printing the result of our code block in each iteration to the R Studio console.
2.For Loop Through character vectors
Syntax written in R Pane :
#For Loop through Character vectors
# First Declaring a Variable name var2
#Iam adding Five person Names as a List to var2 Variable
var2 <- c(“Subha”,”Reshma”, “sri”, “Jo”, “Hareesh”)
#The above var2 Variable creates Character vector
for (i in var2){
#loop the character vectors stored in variable var2
print (paste(“The Name”,i, “consists of”, nchar(i),”characters”))
}
From the above code Variable var2 is assigned to a List of five person Names
And in the body of the loop, we are trying to print the every name of the Person. Number of Characters the name consists.
Note: 1. Paste function is used to concatenate or add the multiple String Values
2. From the above example, nchar(i) represents number of characters in a string
3.For Loop through vector by Appending the Data ( this example will help you to append the data)
Syntax written in R pane:
#For Loop through vector by Appending the Data
#Let us create an empty data Object
var1 <- numeric ()
#Now will use For statement to create a vector of output Values
#Head of For Loop Block
for(i in 1: 10){
#Execute Code Block
var1 <- c(var1,i**2)
print (var1)
4. Nested For Loop:
Code written in console pane :
#Nested Loop
#Create Empty Data Object
var1 <- character()
for(i in 1:5){
#Nested For loop
for(j in 1:3){
var1 <- c(var1,paste(LETTERS[i],letters[j],sep = “_”))
}
}
print(var1)
Here paste Function is used to combine the strings, LETTERS is also a function to display the alphabet in Capitals , letters is also a function to display alphabets in Lower letters, sep is a separator between the Upper case string and lower case string, and separator used here is underscore to separate the strings.
5. Let’s use Break statement in For loop
Break: When the break statement is encountered inside a loop, the loop is immediately terminated, and program control resumes at the next statement following the loop.
6.Next statement in for Loop :
The next statement in R programming language is useful when we want to skip the current iteration of a loop without terminating it. On encountering next, the R parser skips further evaluation and starts next iteration of the loop.
7. Create Multiple Plots within For Loop
Code written in Source Pane :
# Create multiple plots within For Loop
#ncol represents no.of colums in iris dataset
for(i in 1:(ncol(iris)- 1)){
#plot is a function to display the rows & colums in Plot
#nrow represents no.of rows in iris dataset
plot(1:nrow(iris),iris[,i])
#sys.sleep function will suspend the execution of R expressions
#for specified Time Interval, here Time interval is 1
Sys.sleep(1)
}
Please Click on zoom button in the plot pane to see the detailed image.
Note : iris dataset is a famous data set & in built dataset which gives the measurements in centimeters of the variables sepal length and width and petal length and width, respectively.
