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plot histogram without using matlab hist() function

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ws
ws on 22 Dec 2011
Hi all
There is a function called hist(), but if I want to plot a graph without using hist() command, how to plot a graph? I means using command to do the job same as hist().
Thank you.

  2 Comments

Aditi Shetty
Aditi Shetty on 19 Aug 2018
A=imread('<your image path>');
a=rgb2gray(A);
subplot(3,1,1);
imshow(a);
title('original image');
[r,c]=size(a);
z=zeros(1,256);
for i=1:r
for j=1:c
b=a(i,j);
z(b+1)=z(b+1)+1;
end
end
N=sum(z);
p=zeros(1,256);
s=zeros(1,256);
c=zeros(1,256);
r=zeros(1,256);
for k=1:256
p(k)=z(k)/N;
if k==1
c(k)=p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
else
c(k)=c(k-1)+p(k);
s(k)=c(k)*255;
r(k)=floor(s(k));
end
end
subplot(3,1,3)
stem(r,z)
title('histogram')
Ritvik Ramesh Palvankar
Ritvik Ramesh Palvankar on 10 Sep 2019
Hey Adil,
Can you explain me the code after "for k=1:256". I did not understand the part where you took s(k)=c(k)*255
Also, why is zero matrix used and why is c(k-1) added to p(k)

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Accepted Answer

Naz
Naz on 22 Dec 2011
It depends on how you want to bin your data and what kind of data you have.
The idea of hist function is similar to stacks of coins: Let's say you have a bag of coins and after you separate them by values and stack on one another, you will get different heights. The hist function does the same.
data=[1 3 5 7 4 8 0 1 3];
If you want to distribute your data into 10 bins, you would create a new array of size 10:
histArray=zeros(1,10); % prealocate
x=0:1:9;
then, you would run a forloop to count how many times you encounter in a particular value:
for n=1:length(data)
histArray(1,data(n)+1)=histArray(1,data(n)+1)+1; % every time you meet the particular value, you add 1 into to corresponding bin
end
bar(histArray)
There could be another case. Let's say you want to distribute your data into 5 bins only (0 and 1 go in the 1st bin, 2 and 3 go in the 2nd...). In this case, you would run the same loop but with more complicated conditioning:
histArray=zeros(1,5);  %prealocate
x=0:2:8 % create bin numbers for plot
for n=1:length(data)
histArray(1,floor(data(n)/2)+1)=histArray(1,floor(data(n)/2)+1)+1;
% every time you meet the particular value
%you add 1 into to corresponding bin
end
bar(x,histArray)
You can design your own hist function to fit you needs

  2 Comments

ws
ws on 22 Dec 2011
thanks, this is what i'm looking for.. :)
Anna Kasdan
Anna Kasdan on 7 Oct 2018
Hi! I am trying to do this with data that includes negative numbers, and I get the error 'Subscript indices must either be real positive integers or logicals.' Any thoughts? The data I am working with is:
n = 200; a = 0; b = 2; data = b.* randn(1, n) + a;

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More Answers (1)

Adrian Lukasik
Adrian Lukasik on 13 May 2015
Edited: Adrian Lukasik on 13 May 2015
hello I have another problem. The same thing, but in 3D: There is a function called hist3(), but if I want to plot a graph without using hist3() command, how to plot a graph? I means using command to do the job same as hist3(). I have matrix b, 2x1000, and the task about making histogram plot without hist3() function.
Thank you.

  1 Comment

Walter Roberson
Walter Roberson on 13 May 2015
You should open a new Question for that.
Once you have the counts for each grid-point, use bar3()

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