For loop through cell arrays
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I have a 1×4 cell array of
{60×4 double} {60×4 double} {60×4 double} {60×4 double}
and I need to;
-find the values at the 3rd column at the rows have "20" at the first column in each cell
-then eliminate zeros if there is any
-then take average
As an illustration
10 NaN 0 NaN 20 NaN 623 1
10 NaN 0 NaN 20 NaN 0 NaN
20 NaN 310 1 10 NaN 38 1
20 NaN 0 NaN 10 NaN 0 NaN
20 NaN 1445 1 10 NaN 0 NaN
the first cell should give the average of 310 and 1445, whereas the second cell should give 623.
I am thinking of a for loop but I couldnt make it work. Thanks in advance!
3 个评论
Adam Danz
2020-6-23
Could you share your loop so we can help fix it? Otherwise we're doing it for you.
Ali Yilmaz
2020-6-23
Adam Danz
2020-6-25
See answer below.
采纳的回答
If you want to do this in a loop, there are 4 steps I've outlined below.
"c" is the 1x4 cell array.
column3Means = nan(size(c));
for i = 1:numel(c)
% Find rows where column 1 equals 20
index1 = c{i}(:,1) == 20;
% Find rows where column 3 is not 0
index2 = c{i}(:,3) ~= 0;
% Combine those indices
idx = index1 & index2;
% Use the combined index to compute the mean
column3Means(i) = mean(c{i}(idx,3),'omitnan');
end
FYI, the loop can be avoided using the cellfun() function.
10 个评论
madhan ravi
2020-6-25
Wow didn’t know there was a cellarray() function , was it released in 2020a?
Adam Danz
2020-6-25
oops :D typo. I meant cellfun.
Corrected. Thanks, madhan.
Ali Yilmaz
2020-6-25
Ali Yilmaz
2020-6-25
Adam Danz
2020-6-25
Could you share the code you're using to compute the mean?
You probably just need to work in the "nanflag" input to ignore nans in your data.
Ali Yilmaz
2020-6-25
编辑：Adam Danz
2020-6-25
Adam Danz
2020-6-25
You're not using index1. You're also taking the mean of the index rather than using the index to extract the values from zeroback.
But please look at every line and look at the values being produced on each line so you can understand what they are doing.
Try this.
column3Means = nan(size(c));
for i = 1:numel(c)
% Find rows where column 1 equals 20
index1 = c{i}(:,1) == 20;
% Find rows where column 3 is not 0
index2 = c{i}(:,3) ~= 0;
% Combine those indices
idx = index1 & index2;
% Use the combined index to compute the mean
column3Means(i) = mean(c{i}(idx,3),'omitnan')
end
Ali Yilmaz
2020-6-25
Adam Danz
2020-6-25
Glad it worked out.
The take-home message is: learn/use indexing.
Indexing is a superpower of Matlab. My answer uses logical indexing but there are other types of indexing as well.
Ali Yilmaz
2020-6-25
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