Getting The Decimal Part Of A Number In ColdFusion
Posted May 7, 2007 at 8:54 AM
Over the weekend, I was fooling around with ColdFusion date/time values when I thought it would be useful to grab the decimal value of the date (the time part). Then it occurred to me - I don't think I have ever done this before. Now, I don't mean grabbing the actual fraction, I mean getting the integer value that is right of the decimal point.
After some good pacing, the only way to do this I could come up with through ColdFusion string manipulation. Since ColdFusion stores all simple values as strings, this makes manipulating values as strings quite natural. But, even when it came to string manipulation, I found two different ways to do this: one way uses a regular expression to strip out the decimal (and leading zero), the other way treats the value as a decimal-delimited list.
Here is the regular expression version:
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- <cffunction
- name="GetDecimal"
- access="public"
- returntype="numeric"
- output="false"
- hint="Returns the decimal value of the given number (as an integer).">
-
- <!--- Define arguments. --->
- <cfargument
- name="Value"
- type="numeric"
- required="true"
- />
-
- <!---
- Once we have the numeric decimal value, we can
- convert it to a string so that we can use a regular
- expression replace to strip out the starting zero
- and decimal point.
- --->
- <cfreturn
- ToString(
- ARGUMENTS.Value - Fix( ARGUMENTS.Value )
- ).ReplaceFirst(
- "^0?\.",
- ""
- )
- />
- </cffunction>
In this version, I am getting the decimal value but subtracting the fix()'d value from the actual value. This should result in a zero-leading decimal value. Then, I convert it to a string (just in case) and strip out the leading zero and decimal point. This results in the integer form of the decimal:
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- <!--- Get decimal values values. --->
- #GetDecimal( 134.5464 )#
- #GetDecimal( 134 )#
- #GetDecimal( 134.34464 )#
- #GetDecimal( 134.45444554445 )#
... results in:
5464
0
34464
45444554445
Notice that the second value, 134, results in the decimal value, 0.
In this next version, we treat the value as a decimal-point-delimited list. By doing that, we can just grab the last list item to get the decimal value as an integer:
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- <cffunction
- name="GetDecimal2"
- access="public"
- returntype="numeric"
- output="false"
- hint="Returns the decimal value of the given number (as an integer).">
-
- <!--- Define arguments. --->
- <cfargument
- name="Value"
- type="numeric"
- required="true"
- />
-
- <!---
- To get the decimal value, we are going to treate the
- value as a list with a decimal-point delimiter. When
- doing this, we will append our own value to make sure
- that the list has at least TWO (maybe three if there is
- already a decimal place) list items.
- --->
- <cfreturn
- ListGetAt( (ARGUMENTS.Value & ".0"), 2, "." )
- />
- </cffunction>
Ok, so now we have two different approaches, which do we use? Time for some speed tests. Now, I know that I get a lot of crap for running CFLoop speed tests (not true load bearing speed tests), but hey come on, I don't get enough sleep for that sort of thing :) Take it with a grain of salt if you like.
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- <!--- Test the ColdFusion regular expression method. --->
- <cftimer
- type="OUTLINE"
- label="Partial Math Method And RegEx">
-
- <cfloop
- index="intI"
- from="1"
- to="1000"
- step="1">
-
- <!---
- Get a random decimal value to make sure
- that ColdFusion is not just optimizing
- the compiled code.
- --->
- <cfset intDecimal = GetDecimal(
- "1." &
- RandRange( 1, 9 )
- ) />
-
- </cfloop>
-
- </cftimer>
-
-
- <!--- Test the decimal-delimited-list method. --->
- <cftimer
- type="OUTLINE"
- label="Delimited List Method">
-
- <cfloop
- index="intI"
- from="1"
- to="1000"
- step="1">
-
- <!---
- Get a random decimal value to make sure
- that ColdFusion is not just optimizing
- the compiled code.
- --->
- <cfset intDecimal = GetDecimal2(
- "1." &
- RandRange( 1, 9 )
- ) />
-
- </cfloop>
-
- </cftimer>
Running the above speed tests, the delimited list method ran 2 to 3 times faster than the regular expression method (23-47ms vs. 74-123ms). Thinking about it, after the fact, this makes a lot of sense. The list method uses no math and no regular expressions; it just parses the number as a string and grabs part of its value. There is very easy to do. In the first version, I am actually doing math. No wonder it is slower.
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Reader Comments
I didn't do speed tests, but why not this?
<cfset number = 3.14159 />
<cfset decimal = number - int(number) />
<cfdump var="#decimal#">
Posted by Ryan Guill on May 7, 2007 at 9:18 AM
@Ryan,
That gives me:
0.14159
... what I wanted to get was just
14159
But this is basically doing the same thing as my Fix() method. Int() itself makes me a little nervous because it actually rounds, where as Fix() just strips off the decimal.
Posted by Ben Nadel on May 7, 2007 at 9:38 AM
hi try using listLast() a with "." as the delimiter.
Posted by da on May 7, 2007 at 9:54 AM
Good suggestion. ListGetAt(... 2), in this case is the same as ListLast()... but ListLast() is less typing :)
Posted by Ben Nadel on May 7, 2007 at 9:56 AM
Oh wait, no, it;s not the same thing (which is why I didn't use it). Think of this scenario:
4
I append ".0" to that to get:
4.0
ListGetAt(.. 2) in this case is the same as ListLast(). However, if my initial value is:
4.3
... and then I append ".0" to get:
4.3.0,
... then ListGetAt( ... 2) will give me "3", while ListLast() will get me "0".
I need to get ListGetAt() to deal with cases where I have a decimal point already vs. cases where I am dealing with a whole number.
Posted by Ben Nadel on May 7, 2007 at 9:58 AM
You may find this a little more straightforward:
#val(listRest(ARGUMENTS.Value, "."))#
Posted by Nelson Winters on May 7, 2007 at 10:48 AM
@Nelson,
Not a bad idea. Thanks.
Posted by Ben Nadel on May 7, 2007 at 10:51 AM
Why not use REVERSE(FIX(REVERSE(num)))?
Posted by guest on Oct 23, 2007 at 2:02 PM
