Ruby if else in array.each

Question

New to Ruby here. I am attempting to put an if else statement in an array to send a string if a certain modulus == 0. for the life of me i can't find it anywhere. I am sure someone will find it ridiculously simple.

a = *(1..100)
a.each { |i| puts "three" if i % 3 == 0 elsif puts "five" if i % 5 == 0 else puts i}

Just not sure of the correct syntax. Still new to ruby and am trying to learn the syntax. Took a C class last semester and my brain keeps wanting to put in C syntax.

When I leave it as

a = *(1..100)
a.each { |i| puts "three" if i % 3 == 0}

it works fine, just trying to figure out how to add if else to it. Help is appreciated.

The answers below were really helpful. I am trying to take it a step further and call it into a function. It keeps returning 5, and not "five", or 3, and not "three".

here is my function:

def array_mod
a = *(1..100)
a.each { |i| if i % 3 == 0  && i % 5 == 0; i = "fifteen" elsif i % 3 == 0; i = "three" elsif i % 5 == 0; i = "five" else i = i end }

end

and here is my attempt at calling it.

require "minitest/autorun"
require_relative "array_modulus.rb"



class TestArrayFunction < Minitest::Test


def test_array1

    results = array_mod

    assert_equal(100, results.length)
end

def test_array2

    results = array_mod
    assert_equal("three", results[2])
end


end

I was told it is not updating my array. Thanks again.

Answer 1

The syntax of a conditional expression in Ruby is:

if c_1 then e_1 elsif c_2 then e_2 elsif c_3 then e_3 … elsif c_n then e_n else e_nplus1 end

where c_1 … c_n and e_1 … e_nplus1 can be arbitrary Ruby expressions.

It is possible to use an expression separator (i.e. ; or newline) instead of the then keyword to separate the parts of the conditional expression.

With semicolon (this usage is non-idiomatic):

if c_1; e_1 elsif c_2; e_2 elsif c_3; e_3 … elsif c_n; e_n else e_nplus1 end

With newlines:

if c_1
  e_1
elsif c_2
  e_2
elsif c_3
  e_3
# …
elsif c_n
  e_n
else
  e_nplus1
end

If you use newlines, you can optionally also use the then keyword, but that is non-idiomatic, too:

if c_1
then e_1
elsif c_2
then e_2
elsif c_3
then e_3
# …
elsif c_n
then e_n
else
  e_nplus1
end

So, in your case, the correct syntax would be:

# idiomatic
a.each { |i| if i % 3 == 0 then puts "three" elsif i % 5 == 0 then puts "five" else puts i end }

# non-idiomatic
a.each { |i| if i % 3 == 0; puts "three" elsif i % 5 == 0; puts "five" else puts i end }

# idiomatic
a.each { |i|
  if i % 3 == 0
    puts "three"
  elsif i % 5 == 0
    puts "five"
  else
    puts i
  end
}

# non-idiomatic
a.each { |i|
  if i % 3 == 0
  then puts "three"
  elsif i % 5 == 0
  then puts "five"
  else
    puts i
  end
}

However, for such a chain of if / elsif, it is typically more idiomatic to use a case expression:

# idiomatic
case when c_1 then e_1 when c_2 then e_2 when c_3 then e_3 … when c_n then e_n else e_nplus1 end

# non-idiomatic
case when c_1; e_1 when c_2; e_2 when c_3; e_3 … when c_n; e_n else e_nplus1 end

# idiomatic
case
when c_1
  e_1
when c_2
  e_2
when c_3
  e_3
# …
when c_n
  e_n
else
  e_nplus1
end

# non-idiomatic
case
when c_1
then e_1
when c_2
then e_2
when c_3
then e_3
# …
when c_n
then e_n
else
  e_nplus1
end

Which in your case would look like this:

# idiomatic
a.each { |i| case when i % 3 == 0 then puts "three" when i % 5 == 0 then puts "five" else puts i end }

# non-idiomatic
a.each { |i| case when i % 3 == 0; puts "three" when i % 5 == 0; puts "five" else puts i end }

# idiomatic
a.each { |i|
  case
  when i % 3 == 0
    puts "three"
  when i % 5 == 0
    puts "five"
  else
    puts i
  end
}

# non-idiomatic
a.each { |i|
  case
  when i % 3 == 0
  then puts "three"
  when i % 5 == 0
  then puts "five"
  else
    puts i
  end
}

Note that the conditional expressions (both if and case) are expressions, not statements. There are no statements in Ruby, everything is an expression, everything evaluates to a value. A conditional expression evaluates to the value of the expression in the branch that was taken.

So, you could also write it like this:

# idiomatic
a.each { |i| puts(if i % 3 == 0 then "three" elsif i % 5 == 0 then "five" else i end) }

# non-idiomatic
a.each { |i| puts(if i % 3 == 0; "three" elsif i % 5 == 0; "five" else i end) }

# idiomatic
a.each { |i|
  puts(if i % 3 == 0
    "three"
  elsif i % 5 == 0
    "five"
  else
    i
  end)
}

# non-idiomatic
a.each { |i|
  puts(if i % 3 == 0
  then "three"
  elsif i % 5 == 0
  then "five"
  else
    i
  end)
}

# idiomatic
a.each { |i| puts(case when i % 3 == 0 then "three" when i % 5 == 0 then "five" else i end) }

# non-idiomatic
a.each { |i| puts(case when i % 3 == 0; "three" when i % 5 == 0; "five" else i end) }

# idiomatic
a.each { |i|
  puts(case
  when i % 3 == 0
    "three"
  when i % 5 == 0
    "five"
  else
    i
  end)
}

# non-idiomatic
a.each { |i|
  puts(case
  when i % 3 == 0
  then "three"
  when i % 5 == 0
  then "five"
  else
    i
  end)
}

Answer 2

You can use an if to qualify a single statement, but once you move into elsif/else territory, it's necessary to break it up like a normal C-style if statement:

a.each do |i|
  if i % 3 == 0 
    puts "three" 
  elsif i % 5 == 0
    puts "five" 
  else
    puts i
  end
end