how to use ruby " case ... when " with inequalities?

Question

can you do this in ruby? it seems to "miss" the cases with inequalities

 case myvar
 when  myvar < -5
    do somethingA
 when -5..-3
    do special_something_XX
 when -2..-1
    do special_something_YY
 when myvar == 0
    do somethingB
 when myvar > 0
    go somethingC
 end

You can use regex to catch the different cases instead – Flexo Feb 25 '11 at 07:13 — Flexo, Feb 25 '11 at 07:13
@Flexo: Would your approach handle scientific notation? – Andrew Grimm Feb 25 '11 at 07:40 — Andrew Grimm, Feb 25 '11 at 07:40

score 116 · Accepted Answer · answered Feb 25 '11 at 07:20

116

You are mixing two different types of case statements:

case var
when 1
  dosomething
when 2..3
  doSomethingElse
end

case
when var == 1
   doSomething
when var < 12
   doSomethingElse
end

answered Feb 25 '11 at 07:20

toolkit

49,809
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Thank you, that was helpful to me, a relative newbie! – jpw Feb 25 '11 at 09:01
16

wow, all this time i didn't realize the 2nd type existed. thanks. – Doug Feb 25 '11 at 12:27
eli5 written all over it! My favourite kind of explanations :) – Mark Sep 02 '17 at 12:40

score 28 · Answer 2 · edited Dec 11 '12 at 07:33

28

   case myvar
     when  proc { |n| n < -5 }
        do somethingA
     when -5..-3
        do special_something_XX
     when -2..-1
        do special_something_YY
     when proc { |n| n == 0 }
        do somethingB
     when proc { |n| n > 0 }
        go somethingC
     end
   end

edited Dec 11 '12 at 07:33

talha2k

24,937
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answered Dec 11 '12 at 07:16

James Kachiro Sarumaha

390
4
5

12

A few explanations and link would have been nice. – Arnaud Rinquin Dec 11 '12 at 07:35

score 9 · Answer 3 · answered Feb 25 '11 at 07:19

I am not personally convinced that you wouldn't be better off with if statements, but if you want a solution in that form:

Inf = 1.0/0

case myvar
when -Inf..-5
  do somethingA
when -5..-3
  do special_something_XX
when -2..-1
  do special_something_YY
when 0
  do somethingB
when 0..Inf
  do somethingC
end

My preferred solution follows. Here the order matters and you have to repeat the myvar, but it's much harder to leave out cases, you don't have to repeat each bound twice, and the strictness (< vs <= rather than .. vs ...) is much more obvious.

if myvar <= -5
  # less than -5
elsif myvar <= -3
  # between -5 and -3
elsif myvar <= -1
  # between -3 and -1
elsif myvar <= 0
  # between -1 and 0
else
  # larger than 0
end

I personally think that what makes the second alternative clearer are the comments, not the fact that if-elsif is used instead of case-when. That said, I also prefer if-elsif, but just because it is shorter. — kikito, Feb 25 '11 at 10:06

score 4 · Answer 4 · edited Apr 16 '15 at 21:53

4

def project_completion(percent)
 case percent
  when  percent..25
    "danger"
  when percent..50
    "warning"
  when percent..75
    "info"
  when percent..100
    "success"
  else
   "info"
  end
end

edited Apr 16 '15 at 21:53

webdevguy

975
10
17

answered Dec 11 '14 at 08:48

Majid Mushtaq

319
1
3
14

This way seems kind of hackish, and presumably leads to `percent` being compared against itself several times. `case` / `when percent <= 25` / ... seems better (less code/more efficient). It's not necessarily quite as clear that `percent` is the focus of the comparisons, but I think it's easy to see that by looking at the `when` expressions. – mwfearnley Jun 17 '20 at 11:23

score 3 · Answer 5 · answered Aug 02 '16 at 17:41

3

Using infinity may help

case var
when -Float::INFINITY..-1
when 0
when 1..2
when 3..Float::INFINITY
end

answered Aug 02 '16 at 17:41

Vadym Tyemirov

8,288
4
42
38

how to use ruby " case ... when " with inequalities?

5 Answers5

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