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c#.net
hbruce
hbruce

Reputation: 932

How to normalize a list of int values

I have a list of int values:

List<int> histogram;

How do I normalize all values so that the max value in the list is always 100?

Upvotes: 11

Views: 27206

Answers (3)

zomf
zomf

Reputation: 1299

To normalize a set of numbers that may contain negative values,
and to define the normalized scale's range:

List<int> list = new List<int>{-5,-4,-3,-2,-1,0,1,2,3,4,5};
double scaleMin = -1; //the normalized minimum desired
double scaleMax = 1; //the normalized maximum desired

double valueMax = list.Max();
double valueMin = list.Min();
double valueRange = valueMax - valueMin;
double scaleRange = scaleMax - scaleMin;

IEnumerable<double> normalized = 
    list.Select (i =>
        ((scaleRange * (i - valueMin))
            / valueRange)
        + scaleMin);

Upvotes: 9

Bevan
Bevan

Reputation: 44307

If you have a list of strictly positive numbers, then Dav's answer will suit you fine.

If the list can be any numbers at all, then you need to also normalise to a lowerbound.

Assuming an upper bound of 100 and a lower bound of 0, you'll want something like this ...

var max = list.Max();
var min = list.Min();
var range = (double)(max - min);
var normalised 
    = list.Select( i => 100 * (i - min)/range)
        .ToList();

Handling the case where min == max is left as an exercise for the reader ...

Upvotes: 9

Amber
Amber

Reputation: 526623

Iterate though, find the maximum value (call it MAXVAL), then iterate through once more and multiply every value in the list by (100/MAXVAL).

var ratio = 100.0 / list.Max();
var normalizedList = list.Select(i => i * ratio).ToList();

Upvotes: 16

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