Cache values from loop (with differing lengths) to save in 1 variable / matrix

4 次查看(过去 30 天)
I want to calculate the median for time to an event. The 'time to event' is calculated per file in a for loop (so the loop is needed).
Per file there can be multiple 'time to event' values, and the number of values can differ per file.
So, subsequently I want to pool all the time to event values after all files have been processed and to calculate the median for all files.
For example:
file1 = [2;4;6;8]; -> median is 5
file2 = [1;5;10;15]; -> median is 7,5
combined = [2;4;6;8;1;5;10;15]; -> 5,5
for i = 1:length(files)
time_to_event(i) = dataset.time_to_event;
end
median_time_to_event = nanmedian(time_to_event) % use ~NaN
it tells me that the indices of the left side are not compatible with the right side
So, I need a way to combine the generated time to events to in the loop (although they may have different lengths) and then calculate the median.
I was thinking maybe add the time of events of the seperate files in seperate colums and fill the difference in row length with NaN?
But I havent been able to.
Hopefully anybody can help, thanks!

采纳的回答

Voss
Voss 2022-5-29
To handle vectors of different lengths, you can make time_to_event a cell array:
time_to_event = cell(numel(files),1);
for ii = 1:numel(files)
% dateset = data from the ii-th file
time_to_event{ii} = dataset.time_to_event;
end
Then the median of all elements of all time_to_event vectors can be found like this (assuming each one is a column vector like you show in your examples):
median_time_to_event = nanmedian(vertcat(time_to_event{:}));
And the median of each element of time_to_event (i.e., each time-to-event vector) can be found like this:
median_each = cellfun(@nanmedian,time_to_event)
Here's running a concrete case not based on any data:
time_to_event = cell(4,1);
for ii = 1:4
time_to_event{ii} = rand(randi(10),1);
end
disp(time_to_event)
{ 2×1 double} {10×1 double} { 7×1 double} { 3×1 double}
median_time_to_event = nanmedian(vertcat(time_to_event{:}))
median_time_to_event = 0.4235
median_each = cellfun(@nanmedian,time_to_event)
median_each = 4×1
0.5675 0.3538 0.3109 0.4629
  1 个评论
SRRellum
SRRellum 2022-5-29
Thanks for your solution. I saw the above answer of Walter Roberson first and found a similar answer to yours. But comparing mine to yours: yours is way cleaner:)

请先登录,再进行评论。

更多回答(1 个)

Walter Roberson
Walter Roberson 2022-5-29
for i = 1:length(files)
dataset = load something from files(i)
time_to_event{i} = dataset.time_to_event(:);
end
individual_medians = cellfun(@nanmedian, time_to_event);
median_time_to_event = nanmedian(individual_medians);
  1 个评论
SRRellum
SRRellum 2022-5-29
Thanks for you answer.
However, this returned the median of all medians. Which can differ from the median if all values are first taken.
I changed it to the following and works. Maybe not the pretiest solution, but thanks for your help in the proces.
for i = 1:length(files)
dataset.time_to_event = calculating time from alarm to event in files(i)
time_to_event{i} = dataset.time_to_event(:);
end
all_time_to_event = cell2mat({vertcat(time_to_event{:})}); % concatenate different cells + transform cells to double structure
median_time_to_event = nanmedian(all_time_to_event,'all');

请先登录,再进行评论。

类别

Help CenterFile Exchange 中查找有关 Loops and Conditional Statements 的更多信息

产品


版本

R2018b

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by