Sum of array items into another array

I need to find the sum of items within each of the 360 arrays and then make another array with just the sums.

[James Tursa]

You haven't given us enough information to help you. What specific items? How are your arrays stored? You need to give us a short example that shows exactly what you want to do.

[Kirby Fears]

Are your 360 arrays floating around separately in your workspace, or are they all part of one cell array, struct, or ND+1 array?

[np]

they are all separately in the workspace.

ex. data.speed1 data.speed2 . . . data.speed360

they are all 1x30

i want to find the sum of all the thirty items in each and create an other array thats 1x360 that i can plot

[Kirby Fears]

That looks like elements of a struct or columns of a table. What is the type associated with "data" in your workspace?

[np]

its just numbers like ranging from 0 to 0.0170

mostly decimals

[Kirby Fears]

np,

You indicated the data is in your workspace as data.speed1, data.speed2, etc.

In your workspace window, what is the data type of "data"? If it has fields speed1, speed2, etc, then "data" must be a table or struct. Please let me know which type it is so I can help.

[np]

the speed1 speed2 are just the names of the arrays that are there

the values inside of them are numeric

[Kirby Fears]

I understand that the values inside of speed1 and speed2 are numeric, but you wrote your example as "data.speed1". So are speed1 and speed2 contained in a workspace variable called data or not?

Answer 1

[Kirby Fears]

Assuming data is a struct with fields speed1, speed2, etc.

sumArray = structfun(@sum,data);

Answer 2

[Guillaume]

If your structure has fields other than the speed fields, you can loop over a hardcoded number of speed fields:

numspeed = 360;
speedsum = zeros(numspeed, 1);
for speedidx = 1:numspeed
   speedsum(speedidx) = sum(data.(sprintf('speed%d', speedidx)));
end

Answer 3

[Shameer Parmar]

 for i=1:length(fields(data))
     s(i) = sum(eval(['data.speed',num2str(i)]));
 end

[Guillaume]

DO NOT USE EVAL. Please don't provide solutions that use eval, that's just encouraging bad programming practices, particularly when there are better solution.

In this particular case, using dynamic field names does the same without any need for eval:

s(i) = sum(data.(['speed',num2str(i)]));

Also, the proper method for obtaining the fields of a structure is fieldnames. fields is a undocumented function that may disappear or change behaviour in future versions of matlab.

In any case, Kirby's answer is much better.

[Stephen23]

Avoid using eval for trivial code like this. Here is why:

https://www.mathworks.com/matlabcentral/answers/196952-how-to-create-new-variables-in-batches-with-strcat

It would be much better to use the functionality that MATLAB already has to allow fieldnames to be defined via strings:

http://www.mathworks.com/help/matlab/matlab_prog/generate-field-names-from-variables.html

[np]

it says: Reference to non-existent field 'speed361'.

how do i just make it stop at speed360

[np]

i used:

 for i=1:length(fields(data))
   s(i) = sum(data.(['speed',num2str(i)]));
 end

[Guillaume]

1) Use fieldnames instead of fields. That won't solve the immediate problem as they both provide the same result, but fields is not supported whereas fieldnames is.

2) You get this error because your data has fields other than the 360 speed fields.

[Shameer Parmar]

Hello np..

I guess your length of fields(data) is more that 360, that why..

If yes, you can apply one more filter like..

 for i=1:length(fields(data))
   if i<=360
      s(i) = sum(data.(['speed',num2str(i)]));
   end
 end