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perform an action on part of a column in a matrix

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Tali Labovich
Tali Labovich 2016-3-30
评论： Tali Leibovich 2016-3-30
Hello
I have a matrix of 3 columns:
The first column contains some numbers that I want to average
Second, either 1 or 0.
3rd is empty because I want to insert values to this column
for example:
5 0 0
4 0 0
6 0 0
4 1 0
7 0 0
8 0 0
9 0 0
7 1 0
1 0 0
4 0 0
3 0 0
What I need is to define a range according to the second column (from the first to the last zero)
calculate the average of the numbers in these rows in column 1
copy the average to column 4
For example:
the average of 5,4,6 is 5
and the average of 4, 7, 8, 9 is 7
so it should look like this:
5 0 5
4 0 5
6 0 5
7 1 7
8 0 7
9 0 7
My questions are:
1. How can I define such range (from zero to zero without 1)?
2. How can I insert the calculated value (the average) into every corresponding row?
Thank you so much for your help!

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回答（1 个）

goerk
goerk 2016-3-30
M %your matrix
maskData = cumsum(M(:,2));
for i=0:max(maskData)
mask = maskData==i;
meanValue = mean(M(mask,1));
M(mask,3) = meanValue;
end

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