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

2017 12 3
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更新时间：2024 10 4
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0 个投票

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?

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Ameerh
Ameerh 2024-10-4
Write a program in MATLAB using for loop read all the elements of the vector and print them.

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 采纳的回答

Star Strider
Star Strider 2017-12-3

0 个投票

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.

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Eden Crespo
Eden Crespo 2017-12-3
I get this error "error: A(I) = X: X must have the same size as I"
Star Strider
Star Strider 2017-12-3
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
Eden Crespo 2017-12-3
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
Eden Crespo 2017-12-3
nvm I got it to work . Thank you for your help!
Star Strider
Star Strider 2017-12-3
As always, my pleasure!
If my Answer helped you solve your problem, please Accept it!
Ameerh
Ameerh 2024-10-4
Write a program in MATLAB using for loop read all the elements of the vector and print them.
Star Strider
Star Strider 2024-10-4
@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!

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更多回答（1 个）

Stephen23
Stephen23 2017-12-3
编辑：Stephen23 2017-12-3

1 个投票

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

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Eden Crespo
Eden Crespo 2017-12-3
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
Stephen23 2017-12-3
@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
Eden Crespo 2017-12-3
Sorry I am very new to this. Ill try It thank you!

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