Thread: Question about a certain code with the C++ syntax

Originally Posted by Elysia

It solves a problem.
But what is this supposed to do:

average= ((temperature[index-1+index+index+1]/temperature.size()));

Also, please do indent your code properly. It's hard to read.

Sorry Elysia. I am trying to take the average of the point and the 2 surrounding points at that point and divide by 3. If that makes sense.

@Jim: Well I want to make it open for a variable amount of elements. Because later on I will have to use File I/O.

Originally Posted by Elysia

Then,
average = (temperature[index - 1] + temperature[index] + temperature[index + 1] / 3);
Make sure you start from index = 1.

Out of curiosity is there an easy way to do a range per say like in MATLAB you can do it because if there 20 points per say you dont want to write out the long way of doing it.

Originally Posted by Rod Micael

@Jim: Well I want to make it open for a variable amount of elements. Because later on I will have to use File I/O.

First I suggest you review how a moving average, or Boxcar Averaging actually works. Second if you are going to have an unknown number of data elements you should be using the push_back() method of inserting your data elements instead of trying to use a fixed sized vector.

Jim

Originally Posted by Elysia

To answer your question: no. There is no such short-hand syntax in C++. You have to use a loop.

If you want to take the average of N elements, then:
average = std::accumulate(temperature.begin() + index, temperature.begin() + index + N, 0) / N;
Loop from 0 to M - N (where M is number of elements and N number of elements you want to average)

Or

average = std::accumulate(temperature.begin() + index - N/2, temperature.begin() + index + N/2, 0) / N;
Loop from N/2 to M - N/2 (where M is number of elements and N number of elements you want to average)

Disclaimer: This is not tested code.

so the loop would have to be a for loop? If I am correct?

Originally Posted by Elysia

To answer your question: no. There is no such short-hand syntax in C++. You have to use a loop.

If you want to take the average of N elements, then:
average = std::accumulate(temperature.begin() + index, temperature.begin() + index + N, 0) / N;
Loop from 0 to M - N (where M is number of elements and N number of elements you want to average)

Or

average = std::accumulate(temperature.begin() + index - N/2, temperature.begin() + index + N/2, 0) / N;
Loop from N/2 to M - N/2 (where M is number of elements and N number of elements you want to average - 1 [ie if you want to average 3 elements, N = 2])

Disclaimer: This is not tested code.

I will do Jim's advice in am minute but here's my attempt. The only question I have that I have to adjust the number_of_elements_avg accordingly since that's going to vary on how many point averages I want otherwise it wont run. Since no value is being put to number_of_elements_avg.

Code:

for (index ==0; numberofterms-number_of_elements_avg)          {
         average = std::accumulate(temperature.begin()+index,temperature.begin()+index+number_of_elements_avg,0)/number_of_elements_avg;
         }

Thanks Elysia!

Originally Posted by Elysia

It would be better if you posted code that would actually compile...
index == 0 should be int index = 0.
Your are missing index++.
You should initialize number_of_elements_avg to the number you actually want - 1. You can get this from the user or hard-code it. It's up to you.
And be sure to test it!

That's the part I am confused. Why does this need to be number_of_elements_avg-1? If that's what you are saying?

Originally Posted by Elysia

I found more errors, so again, revised code:

average = std::accumulate(temperature.begin() + index - N/2, temperature.begin() + index + N/2 + 1, 0) / (N + 1);

If we say we want to average 3 elements (N=2), then the code becomes:

average = std::accumulate(temperature.begin() + index - 1, temperature.begin() + index + 2, 0) / 3;

If index = 1, then this will average element 0 (index - 1 = 1 - 1 = 0) to 2 (index + 2 = 1 + 2 = 3). Remember that the second argument shall be the argument just after the last one you want to add.
Divide by 3 after that and you have your avg.

Code:

for (int index =0; numberofterms-number_of_elements_avg,index++) 
         {
         average = std::accumulate(temperature.begin() + index - numbers_of_elements/2, temperature.begin() + index + number_of_elements/2 + 1, 0) / (number_of_elements + 1);
         }

Originally Posted by Rod Micael

so here's what I have so far:


Is this just part of the problem or will the inside code need to be changed as well?

Why did you erase what I told you to do? I wasn't wrong either.