MATLAB one-liners
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One of the joys of using MATLAB is that it has a stock of matrix functions like diff, sort, all, and so on, that can be combined in all sorts of interesting ways. For example, in a recent question, the challenge was to find a compact code to determine which columns of a matrix A have all elements equal. Matt Tearle came up with this nifty answer:
all(~diff(A))
What are your favorite one-line MATLAB expressions?
采纳的回答
Walter Roberson
2011-3-3
cell2mat(arrayfun(@(K) accumarray(C, F(:,K), [], @mean), 1:size(F,2), 'Uniform', 0))
In response to a cssm question:
I have a feature matrix, F(m, n) and a cluster vector, C(m, 1).
Now I want to get the mean of feature in F according to C. Make
it simple as below:
F = [2 5; 3 7; 8 4]
C = [2; 1; 2]
output should be [3 7; (2+8)/2 (5+4)/2]
=[3 7; 5 4.5]
2 个评论
Matt Fig
2011-3-3
ARRAYFUN, and ACUMARRAY? About all that is missing is to somehow work BSXFUN in there too!
Andrew Newell
2011-3-28
更多回答（9 个）
Matt Tearle
2011-3-3
I'm a huge fan of logical indexing. Expressions like
mean(frogs(wombats > 42))
rock my world.
3 个评论
Andrew Newell
2011-3-3
Sean de Wolski
2011-3-3
I use the function 'keep' from the FEX which performs the inverse of clear.
I also use the variables 'in', 'out' a lot. So the other day I typed:
'keep out'
which kind of made my day.
Andrew Newell
2011-3-3
Sean de Wolski
2011-3-3
Here's another from a thread today:
Given a connected components analysis (bwconncomp) and some criteria for objects to meet: remove objects that don't meet that criteria from your binary image:
I(cell2mat(CC.PixelIdxList(~idx)')) = false;
1 个评论
Sean de Wolski
2011-3-3
idx can usually be a one line expression from cellfun making this a super-awesome-long-one-liner.
Matt Fig
2011-3-3
groups = mat2cell(A,diff([0;find(diff(A) ~= 1);length(A)]),1);
Pretty Slick.
6 个评论
Andrew Newell
2011-3-3
Matt Fig
2011-3-3
LOL, LI is tops, but not always necessary or useful.
Walter Roberson
2011-3-3
Strange, I am sure I wrote code much like that in response to one of the numerous copies of that question. I cannot seem to find it now, though. I had the 1 first, and I used > instead of ~=
Matt Fig
2011-3-3
I had it stored in my "One liners" file, which is made up of one-liners either I or somebody else on CSSM wrote in response to some question. The file is too big to be much use anymore...
Matt Tearle
2011-3-3
Matt Fig: "LI is tops, but not always necessary or useful"
An unbeliever! Persecute! Kill the heretic!
Walter Roberson
2011-3-3
Ah, I found my copy, and it was _not_ a 1 liner. I had used
b=diff(a); %find differences
idx = find([b 2]>1); %find their indexes
cel = mat2cell(a, 1, [idx(1) diff(idx)]); %break up the matrix
Matt Tearle
2011-3-3
Inspired by something I'm working on right now & your comment to my previous answer...
If you have an n-by-1 structure array people with a field suck (which contains a scalar for each struct element), and you want to find the average:
mean([people.suck])
Extract multiple elements, concatenate, apply function. All in one line.
Oleg Komarov
2011-3-3
eval('fliplr(['''' 33 33 33 33 33 76 105 118 69 32 109 39 73 ''''])')
MuAhahauHAh!!!
3 个评论
Andrew Newell
2011-3-3
Oleg Komarov
2011-3-3
You're the evilest!
the cyclist
2011-3-28
I used to be an admin on a chess server where "qu" could be used as a shorthand to quit out of the interface. A common prank was to tell newbies that "qu" could be used to display the "quote of the day".
Andrew Newell
2011-3-4
3 个评论
Walter Roberson
2011-3-4
sprintf() it and regexrep() on the result, substituting spaces for leading space-zero-space; another regexprep() call could substitute spaces for trailing space-zero-space.
Doug Eastman
2011-3-29
It's not pretty but just for fun, here's one way to do it:
trimmedTriangle = cell2mat(cellfun(@(x) x(1:size(num2str(expm(diag(1:n-1,-1))),2)),cellfun(@(x,y)[x y],cellfun(@(x) repmat(' ',1,x),num2cell(round(linspace(size(num2str(expm(diag(1:n-1,-1))),2)/2,0,n))'),'UniformOutput',false),regexprep(mat2cell(num2str(expm(diag(1:n-1,-1))),ones(n,1)),' 0',' '),'UniformOutput',false),'UniformOutput',false))
Andrew Newell
2011-3-29
Drew Weymouth
2011-3-4
0 个投票
Read in an image and convert it to a grayscale, double matrix of data range 0..1
im= rgb2gray(double(imread('filename.jpg'))/255);
1 个评论
Walter Roberson
2011-3-4
or more generally, rgb2gray(im2double(imread('filename.jpg')))
Your code would fail for images that happened to be already double or happened to be uint16.
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