Rails: performing math on a database integer in controller

Question

I have a some numbers stored in the database.

>> t = Total.first
=> #<Total id: 1, profit: 1058, number: 17, fees: 204, created_at: "2012-01-12 06:44:30", updated_at: "2012-01-12 06:51:13">

I want to perform division on one of the integers (an integer that will be updated frequently) and have the division on the newly updated integer. I basically just want to know what percent the profit is of 26,000

>> t.profit
=> 1058
>> t.profit / 26000
=> 0
>> t.profit.to_i / 26000
=> 0

I was hoping it would be as easy as something like this

def index  
  @t = Total.first
  @x = @t.profit / 26000
end

View

<%= @x %>

but it's not working, as the console suggested it wouldn't. Any hints?

Jordan Running · Accepted Answer · 2012-01-12 08:05:55Z

4

An alternative to Sergio's method is to use Rails' built-in number_to_percentage view helper.

In your controller:

def index  
  @t = Total.first
  @x = @t.profit / 260.0  # = 26000 / 100
end

In your view:

<%= number_to_percentage @x, :precision => 0 %>

Or, if you're not using @t for anything else let the database do the math:

def index
  @t = Total.select('profit / 260 AS profit').first
end

Then...

<%= number_to_percentage @t.profit, :precision => 0 %>

edited Jan 12, 2012 at 8:05

answered Jan 12, 2012 at 7:39

Jordan Running

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6 Comments

Leahcim Over a year ago

Thanks a lot. I looked at number_to_percentage, trying this number_to_percentage(x) but it didn't work. I'll give yours a shot.

Leahcim Over a year ago

Your original solution is giving me 0% in the view when it should say 4%

Leahcim Over a year ago

@x = 0.038461538461538464. this code gave me .04 <%= number_to_percentage @x, :precision => 2 %>

Jordan Running Over a year ago

Oh, I misread the docs. number_to_percentage expects, well, a percent value, e.g. 50 => 50%, not .5 => 50%. I've updated my answer.

Leahcim Over a year ago

I was sort of thinking the same thing, but I didn't do it right. I put this in the controller @x = @t.profit / 26000.0 and then on the next line @x = @x x 10.0 but it didn't allow me to multiply

|

Sergio Tulentsev · Accepted Answer · 2012-01-12 07:29:57Z

2

It's an integer division, so the result is rounded. Convert one of your operands to float.

t.profit / 26000.to_f

To round that to two decimal places use something like this:

"%.2f" % (t.profit / 26000.to_f)

answered Jan 12, 2012 at 7:29

Sergio Tulentsev

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4 Comments

Leahcim Over a year ago

Thanks a lot. Can you make it a human readable number. i.e instead of 0.040692307692307694 I want 4%

Leahcim Over a year ago

O, you wrote your answer to my first comment that i deleted. sorry about that.

Sergio Tulentsev Over a year ago

@Michael: There's the code for "0.04". How to turn it to "4%" - that's gonna be your homework :-)

Leahcim Over a year ago

someone did my homework for me...but to be honest, I did try to get the same solution as him (number_to_percentage) just didn't implement it right.

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