Splitting an array into smaller unequal-sized arrays dependend on array-column values
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Hello all, I'm quite new to MatLab and this problem really drives me insane:
I have a huge array of 2 column and about 31,000 rows. One of the two columns depicts a spatial coordinate on a grid the other one a dependent parameter. What I want to do is the following:
I. I need to split the array into smaller parts defined by the spatial column; let's say the spatial coordinate are ranging from 0 to 500 - I now want arrays that give me the two column values for spatial coordinate 0-10, then 10-20 and so on. This would result in 50 arrays of unequal size that cover a spatial range from 0 to 500.
II. Secondly, I would need to calculate the average values of the resulting columns of every single array so that I obtain per array one 2-dimensional point.
III. Thirdly, I could plot these points and I would be super happy.
Sadly, I'm super confused since I miserably fail at step I. - Maybe there is even an easier way than to split the giant array in so many small arrays - who knows..
I would be really really happy for any suggestion.
Thank you,
Arne
采纳的回答
Using the new histcounts (it works the same with histc)
m=[1 2;2 5;4 7;5 10;6 9;3 3]
[~, ~, indices ] = histcounts(m(:, 2), 0:2:max(m(:, 2)))
mbinned = arrayfun(@(idx) m(indices == idx, :), unique(indices), 'UniformOutput', false)
mcol1 = accumarray(indices, m(:, 1), [], @mean);
mcol2 = accumarray(indices, m(:, 2), [], @mean);
meanbin = [mcol1 mcol2]
更多回答（2 个）
dpb
2014-11-7
One option -- see
doc histc
1 个评论
Andrei Bobrov
2014-11-7
编辑：Andrei Bobrov
2014-11-7
comment by Arne
Thank you :) - I thought of histc as well; but as I said Im rather new to MatLab - so far I only used histc for separating a vector and counting the frequency of certain ranges.
Now, I need to separate for a certain array column and actually obtain the values of both columns not just the counts.
Do you know of a syntax?
E.G.
I have Matrix
1 2
2 5
4 7
5 10
Let's say I'd like to obtain the rows (with actual values) that have column2-value 0-1; 1-2; ... 9-10.
I haven't managed to get to that result with histc. But maybe I have overseen sth..
Arne
2014-11-7
0 个投票
5 个评论
Guillaume
2014-11-7
Please use, the 'Comment on this Answer' button rather than starting a new answer. It's easier to follow the discussion.
If indices (the SUBS of accumarray) is the third output of histcounts (or 2nd of histc) there's no way it can contain non-positive or non-integer values as it's a vector of matrix indices. You must have done something different.
Yes, sorry I made a typo for the 2nd accumarray. It should indeed be column 2. I'll edit the answer.
dpb
2014-11-7
... the indices-vector is just as I expected (its values go from 0 on to positive integer values) - nothing unusual.
But it IS unusual--actually it's more than "unusual" it's wrong. Matlab arrays are (and ever have been and ever shall be, it appears) 1-, not 0-based.
Your indices vector MUST go from 1:N, not 0:N-1
Guillaume
2014-11-7
Ah, 0 is not expected in the indices, since it's not a valid index for a matrix element.
This means that some values are outside the range specified by the bins for histcount. Either you have some values below -430, or more likely, the max is not a multiple of 5,
histcounts(m(:, 2), -430:5:max(m(:, 2))+5)
should solve it.
Arne
2014-11-7
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