Functions within accumarray

Question

If I have a column of dates and a column of data, I use this code to find the cumulative sum of the data for each of the dates, as found in the third column:

orgcumulative=cell2mat(accumarray(day,data,[],@(x){cumsum(x)}));
k=orgcumulative==0;
CVD=orgCVD;
CVD(k)=[];

31,3,3
31,2,5
31,1,6
31,5,11
07,2,2
07,3,4
07,4,9
07,2,11
07,3,14
07,5,19
07,3,22
07,1,23
07,1,24
07,2,26
07,3,29
30,5,5
06,4,4

Now I want to divide each data point within a day by the sum of the data within that day. For example:

31,3,3,3/11
31,2,5,2/11
31,1,6,1/11
31,5,11,5/11    <-- 11 is the sum of data for the 31 date
07,2,2,2/29
07,3,4, %and so on...
07,4,9,
07,2,11,
07,3,14,
07,5,19,
07,3,22,
07,1,23,
07,1,24,
07,2,26,
07,3,29, <-- 29 is the sum of data for the 07 date
30,5,5,1
06,4,4,1

If I try:

fractions=cell2mat(accumarray(day,data,[],@(x){  data/sum(x)  }));

This will divide the entire second column by each of the sums. Is there a way to restrict this so the division only happens for the members of the second column within each day?

erikced · Accepted Answer · 2013-06-24 19:49:52Z

1

Would it not be easier to accumulate the total for each day using accumarray and then use the day array as an index when accessing the accumarray output, like so:

total = accumarray(day, data); % equivalent to accumarray(day, data, [], @sum)
fractions = data ./ total(day);

edited Jun 24, 2013 at 19:49

answered Jun 24, 2013 at 19:42

erikced

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1 Comment

siegel Over a year ago

Thanks a ton. Should have thought of this!

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