There are 2 types of Control/Conditional statements and 3 types of Loop available in R. see below
See Also: Introduction to R/ Basic functions of R
Conditional Statements
1. if ... else
2. ifelse() Function
Loop Statements
1. for loop
2. while loop
3. repeat loop
Related Statements/Topics
1. break
2. next
3. logical expression
Conditional Statements
1. if...else Like other programming languages, the if...else statement is the same in R
NOTE: else if/ else keyword should be placed in the next of closing } of the earlier block.
if(logic_expression) {
stmt.
} else if (logic_expression) {
stmt.
} else {
stmt
}
Example 1
x <- 5
if(x>10) {
print("grater than 10")
}
Example 2
x <- 5
if(x>10) {
print("grater than 10")
} else {
print("less than 10")
}
Example 3
x <- 5
if(x>10) {
print("grater than 10")
} else if (x>5 & x<10) {
print("less than 10 BUT grater than 5")
} else {
print("less than 5")
}
2. ifelse() is a function to use with vector AND the return would be a vector also.
Example 1
x = 1:10
ifelse( x %% 2 == 0 , "even", "odd")
OUTPUT: [1] "odd" "even" "odd" "even" "odd" "even" "odd" "even" "odd" "even"
Loop Statements
1. for loop: the basic is the same as other languages BUT the syntex is different
for ( val in vector/sequence )
{
statement
}
Example 1
v = c(1,2,3,4,5)
for ( x in v )
{
print (x)
}
Example 2: Fibonacci Series upto 10th number
f = c(1,1)
for (x in 1:8) {
f <- c(f, sum( tail(f,2) ) )
}
print(f)
OUTPUT: [1] 1 1 2 3 5 8 13 21 34 55 89 144
Example 3: Nested For Loop - a simple pyramid of numbers
for(x in 1:9){
p = NULL
for(y in 1:x){
p = c(p, y)
}
print(p)
}
OUTPUT:
[1] 1
[1] 1 2
[1] 1 2 3
[1] 1 2 3 4
[1] 1 2 3 4 5
[1] 1 2 3 4 5 6
[1] 1 2 3 4 5 6 7
[1] 1 2 3 4 5 6 7 8
[1] 1 2 3 4 5 6 7 8 9
2. while loop: basic is also same for this one.
while( logic_expression )
{
statement
}
Example 1
x=1
y=10
while(x<y)
{
print(x)
x = x + 1
}
Example 2 : Create a vector with the sum of current value from the first value [ x=1⅀x=n ].
v=1:10
x=1
sumV = NULL
while ( x <= length(v) )
{
sumV = c(sumV , sum( head(v,x) ))
x = x + 1
}
print(v)
print(sumV)
OUTPUT:
v ==> [1] 1 2 3 4 5 6 7 8 9 10
sumV ==> [1] 1 3 6 10 15 21 28 36 45 55
3. repeat loop: it just repeats the block until finding a break statement.
repeat {
statement
}
Example 1:
r = 0
count = 1
repeat {
r = c(r,count)
if(count == 5) { break }
count = count + 1
}
print(r)
OUTPUT: [1] 0 1 2 3 4 5
Related Statements/Topics
1. break: this is like other languages. just break a loop to continue and goto the end of the loop.
2. next: this is like continue of other languages. just continue the next iteration by skipping the following statements.
Example 1:
r=NULL
for (x in 1:20) {
if(x == 5) { next}
if(x == 10) { break}
r = c(r,x)
count = count + 1
}
print(r)
OUTPUT:
In output 5 is missing and loop stopes at 10!
[1] 1 2 3 4 6 7 8 9
3. logical expression: this is also like other languages.
R supports the combination of logical operators..
x > 2 & y <5
x > 2 && y <5
x > 2 | y <5
x > 2 || y <5
for vector:
xV & yV ==> will check all the elements and return a logical vector
xV && yV ==> will check the first elements only and return a logical value
xV || yV ==> will check the first elements only and return a logical value
all logical operators:
&, &&, | ,||, ! (NOT)
