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April 14th, 2015, 11:31 PM  #1 
Newbie Joined: Oct 2014 From: Mars Posts: 27 Thanks: 0  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/valuesMaxvaluesMin) * (destinationsMaxdestinationsMin) So if I do: (4/104) * (1000400) = 400 (which is correct) The problem is when I try to use negative numbers, this formula stops working... Example: (5/100) * (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. 
April 17th, 2015, 12:09 AM  #2 
Senior Member Joined: Apr 2014 From: UK Posts: 776 Thanks: 292 
To work out the destination value, you first need to work out where in the source range your value is. This is achieved by (valuevalueMin)/(valueMaxvalueMin) and gives a value between 0 and 1 Taking the first example of 4, 0 and 10 for value, valueMin and valueMax we get: (44)/(104) = 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: ((valuevalueMin)/(valueMaxvalueMin) * (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 
April 17th, 2015, 10:41 PM  #3 
Newbie Joined: Oct 2014 From: Mars Posts: 27 Thanks: 0 
Thanks very much!! 

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