how to compare an element of array to the rest of the elements

I am trying to compare each element of an array with its subsequent elements and get the count of number of times the current element is greater than the subsequent elements.

the following is my code

     function [ z ] = test(i,size_data, num,j,k,sum )
  % test

num=xlsread('MKdata.xlsx');
size_data=size(num);
j=0
k=0
i=1
for (i=i:size_data)

      if num(i) > num([i+1:size_data])
          j=j+1
      else k=k-1
      end
      i=i+1
  end
  sum=j+k
  end

the test data set i am using is

1733  3002  875  164  1464  1399  1039  1096  1812  2347  575  1393  411  283  1407  1294  1102  1886  3058  4587

results shows that every increment of i adds 1 to k and finally i get k=-20, j=0 whereas it should be 26

please guide me, please point out the mistake in logic or syntax

Answer 1

[Image Analyst]

Wouldn't you just do this (vectorized):

% Define some arbitrary random data
data = randi(9, 1, 20)
% Define the element we're going to consider
index = 3;
% Compare each element of an array with its subsequent elements 
% Get logical index that is true when current element is greater.
itIsGreater = data(index) > data(index+1:end)
% Get the count of number of times the current element is greater than the subsequent elements.
theCount = sum(itIsGreater)

You didn't say in words that you want to do that for all possible starting indexes, but if you do, then put it in a loop and make the count depend on starting index.

% Define some arbitrary random data
data = randi(9, 1, 20)
theCount = zeros(1, length(data));
for index = 1 : length(data)
  % Compare each element of an array with its subsequent elements
  % Get logical index that is true when current element is greater.
  itIsGreater = data(index) > data(index+1:end)
  if ~isempty(itIsGreater) % if there is at least 1 greater...
    % Get the count of number of times the current element is greater than the subsequent elements.
    theCount(index) = sum(itIsGreater)
  end
end
% Print to command window..
theCount

[aboltabol]

Thanks

Answer 2

[Walter Roberson]

When you have

        if num(i) > num([i+1:size_data])

then you are comparing one value to a number of values, which will give you a vector of logical results, 0 for any places it does not hold and 1 for any places it holds. "if" is only considered true if all of the elements it is asked to process are true, so your "if" would be considered true only if num(i) was greater than all of the remaining elements in num.

I cannot tell you how to correct your code because you neglected to indicate the circumstances under which you want j or k to be incremented.

Meanwhile I recommend you look at the documentation for all() and for any()

[aboltabol]

Sir, Thanks for your reply I want j to be incremented each time an element, to which num(i) is being compared, is greater than num(i). if the element is less than num(i) then i want k to be incremented. this has to be done for each element, for all its subsequent elements. so for a series having 20 entries the first entry will be compared to the following 19 entries and the 19th entry will be compared to 20th entry only

Answer 3

[Jos]

As Walter said num(i)>num(i+1:end) compares num(i) to all subsequent elements with result 1 for each time true. You can use this by summing the result, which will give what you want. The code below gives your 26 as answer

size_data=size(num,2);
j=0;
k=0;
for i=1:size_data-1
    j = j + sum(num(i)>num(i+1:end));
    k = k + sum(num(i)<num(i+1:end));
end
sum=k-j;

[aboltabol]

Thanks