if - else if - else statement and brackets

Question

I understand the usual way to write an \"if - else if\" statement is as follow:

if (2==1) {
  print(\"1\")
} else if (2==2) {
  print(\"2\")
} else {
  print         


        

Answer 1

In R, also we have ifelse() function:

ifelse(1 < 0, "hello", "hi")

Output:

# [1] "hi"

Answer 2

As hrbrmstr has mentioned:

When the initial if is followed by a compound expression (indicated by the {} pair) the parser by default is going to expect the expression followed by else to be compound as well. The only defined use of else is with compound expressions.

In the statement if(cond) cons.expr else alt.expr, the else needs to be put after and in same line with the end `cons.expr' compound.

So if you want to have your code a better look without brackets, apply this way:

if (2==1) print("1") else 
   if (2==2) print("2") else 
      print("3")

Answer 3

ifelse has tree parametes, first conditon, second true result and last false result.

y_pred = ifelse(prob_predict > 0.5,1,0)

Answer 4

R reads these commands line by line, so it thinks you're done after executing the expression after the if statement. Remember, you can use if without adding else.

Your third example will work in a function, because the whole function is defined before being executed, so R knows it wasn't done yet (after if() do).