wrong values in histogram plotting

Question

Elinor Ginzburg 2023-12-27

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/2064332-wrong-values-in-histogram-plotting

评论： Elinor Ginzburg 2023-12-27

Hello,

I'm trying to plot a histogram of an array. I have a csv file with a list of double values, and I want to see how many elements have a value that is less or equal to 10% of the maximal value, 20%, 30% and etc.. I tried using the following code, but I get wrong statistics, when I check how many elements have a lesser or equal value to 10% of the maximal element, I see that there are 11173940 such elements. I did so by using the following code:

maxElement = max(array);

elementCount = sum(array < maxElement * 0.1);

when I print the histogram it shows like there are less than 180 elements that constitute this condition. this is the code I used (I have a lot of csv files that I want to read and analyze in the same manner, that's why the filename loop):

clear; clc;

dataDir = 'hist_res_rel';

fileList = dir(strcat(dataDir, '/*.csv'));

plotDir = 'plot_dir_rel';

for i = 1:numel(fileList)

fileName = fileList(i).name;

epoch = fileName(length(fileName)-5:length(fileName)-4);

if contains(fileName,'a_rel')

plot_title = strcat('A Realtive Value Change Between Epochs: ', epoch, '-', num2str(str2double(epoch)+10));

end

if contains(fileName,'b_rel')

plot_title = strcat('B Realtive Value Change Between Epochs: ', epoch, '-', num2str(str2double(epoch)+10));

end

rel_val = readmatrix(strcat(dataDir, fileName));

rel_val = abs(rel_val);

Max = max(rel_val);

p = 0.1;

x = zeros(10, 1);

y = zeros(10, 1);

for index = 1:10

percentage = Max * p;

x(index) = percentage;

if index == 1

y(index) = sum(rel_val <= x(index));

else

y(index) = sum(rel_val <= x(index) & rel_val > x(index-1));

end

p = p + 0.1;

end

f = histogram(rel_val, x);

xticks(x);

title(plot_title);

xlabel('Percantage of Relative Change');

ylabel('Amount of Parameters');

xticklabels({'0', '10','20','30', '40', '50', '60', '70', '80', '90', '100'});

saveas(f, strcat(plotDir, '/plot_', fileName(1:length(fileName)-3), '.jpg'));

end

this is the histogram that I get:

and this is the csv file that I'm trying to analyze just to make sure everything works (sorry, it's so large I had to use an external site for the upload):

https://www.transfernow.net/dl/csv_file_data_link

Thank you so much for your time and attention, I appreciate your help.

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Answer 1

Ganesh 2023-12-27

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此回答的直接链接

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在 MATLAB Online 中打开

Hi @Elinor Ginzburg,

I understand that your histogram is inconsistent with the data you have. The issue you are facing can be easily resolved by adding 0 at the start of the variable "x".

When using a histogram, the histogram calculates the number of data points between edges. As your variable "x" begins with Max*0.1, the histogram plots interval between Max*0.1 and Max*0.2 and so on. By adding 0 at the start you can make the first edge to be 0, Max*0.1, which will give you the right result.

x = [0;x] % Add this line before plotting the histogram

Kindly refer to the following document for more information and examples on using the "histogram()" function:

https://in.mathworks.com/help/matlab/ref/matlab.graphics.chart.primitive.histogram.html

Hope this helps!