reduce matrix data by combining values
1 次查看(过去 30 天)
显示 更早的评论
Dear matlab community,
I need to reduce data in a matrix of two columns, and many rows (almost 2 billion, so I would like to find a way to automate it!)
The structure is as follows:
Column 1 has a bunch of discrete values, which occur repeatedly.
Example:
a
b
a
c
b
Column 2 has values in it, that should be added up for all "a", all "b", and all "c", that only one "a", "b", "c" is left in the final matrix.
Example:
Initial matrix:
a 10
b 5
a 1
c 20
b 3
The final matrix should look like this:
a 11
b 8
c 20
Thank you very much! A solution would help me a lot!
0 个评论
采纳的回答
Walter Roberson
2016-3-1
In the below code I assume your array is a cell array (because you cannot mix letters and numbers in a numeric array).
[unique_keys, ~, idx] = unique(YourArray(:,1));
vals_to_total = cell2mat( YourArray(:,2) );
totals = accumarray(idx, vals_to_total);
results = [unique_keys, num2cell(totals)];
3 个评论
Walter Roberson
2016-3-1
If your array is numeric instead of a cell array, then
[unique_keys, ~, idx] = unique(YourArray(:,1));
vals_to_total = YourArray(:,2);
totals = accumarray(idx, vals_to_total);
results = [unique_keys, totals];
You did not show enough of the error message for me to see what it is complaining about.
Is it possible that your data is a MATLAB table() or dataset() data type, or something other than numeric or a cell array?
Also watch out: you assigned to "dx" in the unique() line, but you use "idx" in the accumaray()
更多回答(0 个)
另请参阅
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!