CODEWITHSUNDEEP
arraysmatlab
Bowecho
Bowecho

Reputation: 909

Compute means between time steps for given duration values in MATLAB

For example, I have 5 time steps and a duration value: 

TimeSteps = [4, 5, 6, 7, 8, 10, 11, 12, 14, 15, 16];
Duration = [5, 3, 3];

I want to automatically generate the means between the time steps for every duration. In this case, the result would look like this: 

Result = [mean([4, 5, 6, 7, 8]), mean([10, 11, 12]), mean([14, 15, 16])];

This will lead to: 

Result = [6, 11, 15];

I have a 474x1 duration vector, so I need to automatize this. If anyone can help, it would be great. Thank you.

Upvotes: 4

Views: 149

Answers (3)

Divakar
Divakar

Reputation: 221644

Using bsxfun's masking capability -

%// Setup mask to be used to map Timesteps values onto a 2D matrix
mask = bsxfun(@ge,Duration(:).',[1:max(Duration)]') %//'

%// Initiliaze the 2D matrix where Timesteps values would be put with NaNs
vals = nan(size(mask))
%// Now, put those values
vals(mask) = TimeSteps

%// Find mean along columns for the final output
Result = nanmean(vals,1)

Output -

Result =
     6    11    15

Upvotes: 3

Luis Mendo
Luis Mendo

Reputation: 112749

It can be done easily with accumarray. This works for row or column vectors.

ind = [];
ind(cumsum(Duration(end:-1:1))) = 1;
ind = cumsum(ind(end:-1:1)); %// generate grouping index for accumarray
Result = (accumarray(ind(:), TimeSteps(:))./Duration(:)).';

Upvotes: 4

user2271770
user2271770

Reputation:

You need to apply the mean function to a partition of your TimeSteps that has the sizes in Duration:

Partition = mat2cell(TimeSteps, 1, Duration);
Result    = cellfun(@mean, Partition)

If you're a fan of one-liners:

Result = cellfun(@mean, mat2cell(TimeSteps, 1, Duration));

Note: Please take in account that this solution is posted for row vectors; change the mat2cell call for column vectors.

Upvotes: 5

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