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R IF Else Statement


Syntax: if (condition) {...} else {...}. && and || can be used in the condition. If else statement can be nested.


Let's create a vector containing number 1-10:
>samples <- c(rep(1:10))
>samples
 [1]  1  2  3  4  5  6  7  8  9 10

Print out those sample numbers that are even using if else statement:
>for (thissample in samples)
+{
+    if (thissample %% 2 != 0) next
+    else print(thissample)
+}
[1] 2
[1] 4
[1] 6
[1] 8
[1] 10

The ifelse function is a vectorized version of if else statement. It's syntax is ifelse(condition,v1,v2). if contidion is true, return v1, otherwise v2.

If we want all samples with number >6 be number 2, and those not be number 1, just:
>ret<-ifelse(samples>6,2,1)
>ret
 [1] 1 1 1 1 1 1 2 2 2 2