How can I write a loop that performs a function to each element in a vector?

say I have a vector with numbers 234 456 687 643 23 45 and have a function which can only take one value at a time. How would I loop to call the function to each one of the values individually?

[Ameerh]

Write a program in MATLAB using for loop read all the elements of the vector and print them.

Answer 1

[Star Strider]

Ideally, you would write your function so that it would allow vectorized operations.

If that is not an option try something like this:

Result = zeros(1:length(vector));               % Preallocate
for k1 = 1:length(vector)
    Result(k1) = YourFunction(vector(k1));
end

The length call could be replaced by size (with the appropriate dimension argument), or numel. They all have their appropriate uses, depending on your array.

[Eden Crespo]

I get this error "error: A(I) = X: X must have the same size as I"

[Star Strider]

I have no idea what your function creates.

When in doubt, use a cell array:

Result = cell(size(vector));                 % Preallocate
for k1 = 1:length(vector)
    Result{k1} = YourFunction(vector(k1));
end

See the documentation on Access Data in Cell Array (link) and related topics to work with the cell array.

[Eden Crespo]

Thanks for the help! For future reference, why doesn't the arrayfun work on this function

function Name = GetStationName(id) filename = 'divvy-names.csv';

if exist(filename, 'file') ~= 2  %%doesn't exist:
    fprintf('**Error in GetStationName: cannot find "divvy-names.csv" file\n');
    Name = '?';
    return;
end

%%load file of station names, and search for matching id:
%%MATLAB:
%%names = dataset('File', filename, 'Delimiter', ',');
%%LI = (names.ID == id);

%%this works in MATLAB or Octave:
[IDs, Names] = textread('divvy-names.csv', '%d %s', 'delimiter', ',');
LI = (IDs == id);

if sum(LI) == 0  %%not found:
    Name = 'Unknown station name';
elseif sum(LI) == 1       %%found match:
    I = find(IDs == id);  %%what index was match?
    Name = Names{I};      %%use { } to extract string @ that index:
else  %%found multiple matches, should never happen:
    Name = 'Multiple station names found, something is wrong...';
end
end

if true
  % code
end

[Eden Crespo]

nvm I got it to work . Thank you for your help!

[Star Strider]

As always, my pleasure!

If my Answer helped you solve your problem, please Accept it!

[Ameerh]

Write a program in MATLAB using for loop read all the elements of the vector and print them.

[Star Strider]

@Ameerh — Do exactly that. If you have problems, post a new Question with your code and describe the problem you are having with it.

I will not do your homeework for you!

Answer 2

[Stephen23]

Either use a for loop or arrayfun:

vec = [234,456,687,643,23,45];
arrayfun(@fun,vec)

You might also like to read this:

https://www.mathworks.com/help/matlab/matlab_prog/vectorization.html

[Eden Crespo]

I get this error when trying the arrayfun "error: arrayfun: all values must be scalars when UniformOutput = true" any Idea what the problem is?

[Stephen23]

@Eden Crespo: your function returns non-scalar output arguments. Simply read the error message and do exactly what it states, that will solve the problem:

arrayfun(@fun,vec,'UniformOutput',false)

[Eden Crespo]

Sorry I am very new to this. Ill try It thank you!