accumarray is a MATLAB function that is used to accumulate elements in a vector or matrix based on another vector or matrix of indices. accumarray is commonly used for calculating histograms, grouping values based on certain criteria or applying specific functions to grouped data once they are grouped with accumarray. It is currently one of the most versatile functions in MATLAB's native library and was available since MATLAB 7, R14.
Questions tagged [accumarray]
66 questions
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Improve code / remove for-loop when using accumarray MATLAB
I have the following piece of code that is quite slow to compute the percentiles from a data set ("DATA"), because the input matrices are large ("Data" is approx. 500.000 long with 10080 unique values assigned from "Indices").
Is there a…
Jonas
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Using accumarray to sum data in Matlab
I have a matrix like this:
>>D=[1,0,10;3,1,12;3,1,12.5;6,1,6;6,2,11.1;]
D =
1.0000 0 10.0000
3.0000 1.0000 12.0000
3.0000 1.0000 12.5000
6.0000 1.0000 6.0000
6.0000 2.0000 11.1000
I want to get the sum of the second…
Natalia
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Matlab using accumarray with cell array
I am quite new to Matlab, but I have some experience with other programming languages. I have a very large table imported from MySQL in Matlab. It is given as cell array that looks something like this:
date key sales weight name
12/11 …
user3193435
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Calculating a 2D joint probability distribution
I have many points inside a square. I want to partition the square in many small rectangles and check how many points fall in each rectangle, i.e. I want to compute the joint probability distribution of the points. I am reporting a couple of common…
user2875617
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Fun depending on order of subs and values in accumarray
In accumarray() the first note about 'subs', first appeared in the MATLAB R14sp3 docs, says:
Note If the subscripts in subs are not sorted, fun should not depend on the order of the values in its input data.
It is not clear to me what is…
Oleg
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Matlab Accumarray for 3D matrix
I really wish the documentation was more clear on the use of accumarray for N-D size matrices in Matlab. Regardless, I'm totally confused here and looking for some advice. Here's the challenge:
I have a 3D matrix of data.
ROWS are individual…
tdiddy
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Vectorization using accumarray
I want to project the texture of 3D surface (CylCoors 300000x3) into a 2D plane (Image 380x360). For doing so I take every unique value in Z (UniqueZ=unique(CylCoors(:,3))) and and Theta (UniqueTheta=unique(CylCoors(:,1))) and project all the…
McMa
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Summing rows by index using accumarray
Can I sum rows or columns over several indices without using a for loop?
I have an n by n matrix, M, that represents the co-occurrence of vocabulary terms where n is the length of the vocabulary.
I also have a n by n logical mask, L, which…
Cecilia
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Cumulative sum matlab for loop
I am trying to cumulatively sum consecutive hours(variables 'hrs') between hurricane observations for all observations in a particular storm and among multiple storms in order to determine the duration of the storm. This is what I have:
stormid =…
runnere127
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Using accumarray and @min to extract min from groups but also output corresponding values from another variable/column
I have 3 columns of data:
time = [1;2;3;4;5;6;7;8;9;10;11;12;13;14;15;16];
category = [1;1;1;1;2;2;2;2;3; 3; 3; 3; 4; 4; 4; 4];
data = [1;1;0;1;2;2;1;2;3; 3; 2; 3; 4; 4; 4; 3];
I am using the following to extract the minimum data values for…
Jo.
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How to convert decimal hour and calculate the average every 5 min?
I'm a beginner at Matlab and I need to solve a problem. First, I need to convert the UT columm from decimal hour to hour:minute:seconds. Then, I need to calculate every 5 minutes on average the ROT collumn and show the reply in a new matrix…
Marcelo Duarte
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Find row-wise minima in sparse matrix
I would like to get the minimum nonzero values per row in a sparse matrix. Solutions I found for dense matrices suggested masking out the zero values by setting them to NaN or Inf. However, this obviously doesn't work for sparse matrices.
Ideally, I…
Lisa
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MatLab accumarray unexpectedly changing ordering
As long as I understood accumarray, it means "Making the nth row of the output: 1) find n in sub. 2) if n is in m1, m2, m3 th element in sub, 3) apply the function to m1,m2,m3 th element of val 4) that's the nth row of the output"
Am I wrong…
user1849133
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matlab - only keep days where 24 values exist
Say that I have a dataset:
Jday = datenum('2009-01-01 00:00','yyyy-mm-dd HH:MM'):1/24:...
datenum('2009-01-05 23:00','yyyy-mm-dd HH:MM');
DateV = datevec(Jday);
DateV(4,:) = [];
DateV(15,:) = [];
DateV(95,:) = [];
Dat =…
Emma
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Count number of observations by group matlab
I have a matlab dataset that looks like this:
year value
1995 90000
1995 53000
1995 80000
1995 60000
1995 37000
1995 42000
1995 13102
1996 35000
1996 50000
1996 32000
1996 47000
1997 36000
1997 90000
1997 …
phdstudent
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