Let us first see how if and else work in R. The general syntax for an if clause is given here:

if (expression) { 
   statement 
} 

If an expression is correct then the statement gets executed else nothing happens. An expression can be a logical or numeric vector. In the case of numeric vectors, 0 is taken as False and the rest are taken as True, for example:

>x<-5 
>if(x>0) 
>+ { 
>+ print(" I am Positive") 
>+ } 

When the preceding code gets executed then it prints I am Positive.

Now let us see how the if and else conditions work in R. Here is the syntax:

if(expression){ 
   statement1 
} else { 
   statement2 
} 

The else part is evaluated in case if the if part is False, for example:

> x<--5 
> if(x>0) 
>+ { 
>+ print(" I am Positive") 
>+ }else 
>+{ 
>+ print(" I am Negative") 
>+} 

When the preceding code gets executed, it prints I am Negative.

These loops are executed for a defined number of times and are controlled by a counter or index and incremented at each cycle. Please find here the syntax of the for loop construct:

for (val in sequence) { 
    statement 
} 

Here is an example:

>Var <- c(3,6,8,9,11,16) 
>counter <- 0 
>for (val in Var) { 
>+    if(val %% 2 != 0)  counter = counter+1 
>+} 
print(counter) 

When the preceding code gets executed, it counts the number of odd numbers present in vector c, that is, 3.

while loops are the loops which are set at onset for verifying the logical condition. The logical condition is tested at the start of the loop construct. Here is the syntax:

while (expression) { 
   statement 
} 

Here, the expression is evaluated first and, if it is true, the body of the for loop gets executed. Here is an example:

>Var <- c("Hello") 
>counter <- 4 
>while (counter < 7) { 
>+   print(Var) 
>+   counter = counter+ 1 
>+} 

Here, first the expression gets evaluated and, if it is true, the body of the loop gets executed and it keeps executing till the expression returns False.

apply() is a function in R used for quick operations on a matrix, vector, or array and can be executed on rows, columns, and on both together. Now let us try to find the sum of rows of a matrix using the apply function. Let us execute the following code:

> sample = matrix(c(1:10), nrow = 5 , ncol = 2) 
> apply(sample, 1,sum) 

It generates the sum row-wise.

sapply() operates over a set of data such as a list or vector, and calls the specified function for each item. Let us execute the following code to check the example:

> sapply(1:5, function(x) x^3) 

It computes cubes for 1 to 5.