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April 15th, 2015, 12:31 AM   #1
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Question Transform a number?

Hi, can someone please help me to write a formula to transform a number.

I'm trying to write a function with 5 parameters:
1) The value to be transformed
2) The values minimum range
3) The values maximum range
4) The destinations minimum range
5) The destinations maximum range

For example, lets say I have a value 4 (which belongs in a system that goes from 4 to 10), and I want to transform it into a number (newValue) which ranges from 400 to 1000.

At the moment, this is the formula I have:
newValue = (value/valuesMax-valuesMin) * (destinationsMax-destinationsMin)

So if I do: (4/10-4) * (1000-400) = 400 (which is correct)

The problem is when I try to use negative numbers, this formula stops working...

Example: (5/10-0) * (1 - -1) = 1 (which is wrong. Should be 0 since 0 is the middle of -1 and 1, and the values we gave it were 5 in a range of 0 to 10).

Thanks in advance,
A.
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April 17th, 2015, 01:09 AM   #2
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To work out the destination value, you first need to work out where in the source range your value is.
This is achieved by (value-valueMin)/(valueMax-valueMin) and gives a value between 0 and 1
Taking the first example of 4, 0 and 10 for value, valueMin and valueMax we get:
(4-4)/(10-4) = 0, which is correct as it is at the bottom of your range.
Next we need to convert this range value to a position in your destination range, which is achieved by:
(range * (DesinationMax - DestinationMin) ) + DestinationMin
So, again with the first example we get:
(0 * (1000 - 400) ) + 400 = 400, which is correct.

Putting both parts together we get:
((value-valueMin)/(valueMax-valueMin) * (DesinationMax - DestinationMin) ) + DestinationMin

Now if we try the 2nd example with 5, 0, 10, -1 and 1 for the 5 variables, we get:

((5 - 0)/(10 - 0) * (1 - -1)) + -1 = 0, which is correct
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April 17th, 2015, 11:41 PM   #3
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Thanks very much!!
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