How can I create histograms of relative frequency?

I want to create a histogram of the relative frequency count over regualar intervals.

The relative frequency is the number of instances of data in a particular range divided by the total number of data points.

Answer 1

[MathWorks Support Team]

The following example plots a bar chart of the relative frequency of data "y" in the data range -8 to 94 at intervals of 17.

The data is as follows:

 y = [45 40 28 51 18 35 29 21 29 22 38 24 34 37 43 44 48 ...

     28 9 41 31 40 24 17 15 37 33 35 28 25 25 31 29 44 ...

     41 43 29 25 45 17 61 94 51 39 50 37 40 64 34 20];

Calculating the desired interval width, and creating the desired data range:

numIntervals = 5;

intervalWidth = (max(y) - min(y))/numIntervals;

x = -8:intervalWidth:94;

Next, use the HISTC function to find the frequency of each data range "x" in the given data set "y". This function returns the histogram count for a data set and range.

ncount = histc(y,x);

Calculate the relative frequency of each data range by dividing the frequency by the total number of data points:

relativefreq = ncount/length(y);

Finally plot the relative frequency versus the data ranges as a bar chart. On this chart, the bars will be adjoining, and the tick marks on the x-axis will label the extent of each bar's data range.

bar(x-intervalWidth/2, relativefreq,1)

xlim([min(x) max(x)])

set(gca, 'xtick', x)

Note that the BAR function centers the bars it creates on the supplied x-data. So this data has been translated by half an interval so the extents of the bar width fall on the limits of the data ranges.