How can i sort data using logical indexing?
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problem: i have two arrays: the first one is of unknown lenght and has two columns, one containing the data that i want to add to my second array and one containing a natural number (ranging from 1 to unknown) looking like this:
[ 0] [3]
[ 0] [5]
[ 3.36] [ 2]
[ 0.00100000000000122] [ 6]
[0.000999999999999446] [ 4]
[0.000999999999999446] [ 2]
my second array is empty. now i want to add the values (first columns) to the associated row ( second column) in my second array. There are multiple values for each row. the output of the second array should look like this:
[] []
[3.36] [0.00099999999446]
[0] []
[0.0009999999999446] []
[0] []
[0.00100000000000122] []
Is there a way to do this using logical indexing? It would be nice if i could avoid using for loops with if statements
Thanks.
2 个评论
the cyclist
2016-1-7
Can you write explicitly what you want the output to be, for this example?
Timo Merker
2016-1-7
采纳的回答
Guillaume
2016-1-7
a = [0 3
0 5
3.36000000000000 2
0.00100000000000122 6
0.000999999999999446 4
0.000999999999999446 2];
b = accumarray(a(:, 2), a(:, 1), [], @(v) {v.'})
This creates a 1d (column) cell array where each row is all the numbers corresponding to that particular row index. Each row is just long enough to store the required numbers
The problem comes from you wanting a 2d cell array instead. To be honest, I'm not sure there's any advantage in it and it requires more work. One way of generating it:
%continuing from above
maxcols = max(cellfun(@numel, b)); %or you could get that from the histogram of a(:, 2)
c = cellfun(@(v) [num2cell(v), cell(1, maxcols - numel(v))], b, 'UniformOutput', false);
c = vertcat(c{:})
3 个评论
Timo Merker
2016-1-7
Guillaume
2016-1-7
It's important to use valid syntax in your question to avoid confusion. From your description, I assumed that the input array is a standard array (i.e. matrix), not a cell array.
Now, why is your input a cell array? and more importantly, why does it have empty cells in the first column?
If the cell is empty, it's not going to contribute anything to the output, so you might as well remove that row. Once the input cell array has no empty rows, you can just convert it to a matrix and my answer will work:
a = {0 3
0 5
[] 3
3.36000000000000 2
0.00100000000000122 6
0.000999999999999446 4
0.000999999999999446 2}; %a is now a cell array not a matrix
a(any(cellfun(@isempty, a), 2), :) = []; %remove rows with empty values
a = cell2mat(a)
%now you can use accumarray
Timo Merker
2016-1-7
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