In Matlab, I have two matrices: one with integers,x, and one with booleans, y:
x =
2 4 2
3 3 1
4 1 5
y =
0 0 1
1 1 0
1 0 1
What I now want to do is to assign some elements of x to 5, and I want to use y as a mask to determine which elements should be set to 5. So elements with a corresponding value of 0 in y should remain as they are in x, but those with a corresponding value of 1 in y should be set to 5. Therefore, the output should be:
2 4 5
5 5 1
5 1 5
I have tried the following:
x(y) = 5
Which gives me the error:
Subscript indices must either be real positive integers or logicals.
And I have also tried:
y(x) = 5
Which gives me the following:
5 5 1
5 1 0
5 0 1
Can somebody please explain what is going on here, and what I need to do to get my desired result?
The error you've got is due to the fact that, apparently, y is of type double while, in this case, it should be of type logical
You could try:
x(logical(y))=5
Hope this helps
Its not a fancy solution but will solve your problem
>> x = [ 2 4 2;3 3 1;4 1 5];
y = logical([ 0 0 1;1 1 0;1 0 1]);
f = x(:);
f(y(:)) = 5;
x = reshape(f,size(x))
x =
2 4 5
5 5 1
5 1 5
>>
x(find(y)) = 5; should work fine.
Related
I am new to Matlab and I have a basic question.
I have this data set:
1 2 3
4 5 7
5 2 7
1 2 3
6 5 3
I am trying to calculate the relative frequencies from the dataset above
specifically calculating the relative frequency of x=1, y=2 and z=3
my code is:
data = load('datasetReduced.txt')
X = data(:, 1)
Y = data(:, 2)
Z = data(:, 3)
f = 0;
for i=1:5
if X == 1 & Y == 2 & Z == 3
s = 1;
else
s = 0;
end
f = f + s;
end
f
r = f/5
it is giving me a 0 result.
How can the code be corrected??
thanks,
Shosho
Your issue is likely that you are comparing floating point numbers using the == operator which is likely to fail due to floating point errors.
A faster way to do this would be to use ismember with the 'rows' option which will result in a logical array that you can then sum to get the total number of rows that matched and divide by the total number of rows.
tf = ismember(data, [1 2 3], 'rows');
relFreq = sum(tf) / numel(tf);
I think you want to count frequency of each instance, So try this
data = [1 2 3
4 5 7
5 2 7
1 2 3
6 5 3];
[counts,centers] = hist(data , unique(data))
Where centers is your unique instances and counts is count of each of them. The result should be as follow:
counts =
2 0 0
0 3 0
0 0 3
1 0 0
1 2 0
1 0 0
0 0 2
centers =
1 2 3 4 5 6 7
That it means you have 7 unique instances, from 1 to 7 and there is two 1s in first column and there is not any 1s in second and third and etc.
I am trying to compare 2 vectors to discover if they share 4 consecutive values.
For example
w = [6 7 8 9 10 11 12 13 14]
v = [5 6 7 8 9]
Has 4 consecutive values 6 7 8 9
But
x = [6 7 8 9 10 11 12 13 14]
y = [6 7 1 2 3 4 5 6 13 14]
has four identical values (6 7 13 14) but they aren't consecutive.
The code I am currently using is:
if length(intersect(v, w)) >= 4
condition = true;
but this doesn't test for consecutive elements, so it would return true for both cases listed above whereas I want it to only return true for the first case.
Can somebody please help me find a way to test for identical consecutive elements rather than just identical elements.
Building on Marcos' answer:
Create all possible search vectors from your initial search (i.e. [5 6 7 8] [6 7 8 9]) - however we will make it a 3D matrix which will be m-by-1-by-n
n = 4;
m = numel(v)-n+1;
V = permute(v(bsxfun(#plus,(0:m-1)',1:n)),[1,3,2])
Check if any of these sub-vectors are a subset of the vector being searched
check = sum(any(bsxfun(#eq, V, w),3),2) >= n;
match = squeeze(V(check,:,:))' %'// The ' is debatable here, it depends on how many matches you get
you can compare
bsxfun(#eq, w,v')
Resulting with
ans =
0 0 0 0 0 0 0 0 0
1 0 0 0 0 0 0 0 0
0 1 0 0 0 0 0 0 0
0 0 1 0 0 0 0 0 0
0 0 0 1 0 0 0 0 0
As you can see four consecutive matching elements form a diagonal of length 4.
To find the location of this diagonal you can conv2 with a 4 diagonal filter (eye(4)):
[rr cc] = find( conv2( single(bsxfun(#eq, [1 2 3 w],v')), eye(4), 'same' ) == 4 )
compensating for the center of the filter
loc_in_w = cc - 1
loc_in_v = rr - 1
yielding
loc_in_w =
1
loc_in_v =
2
which are the first index of the sequence in w and v respectively.
This method can work with more than one occurrence of a 4-substring of v in w...
I haven't meddled in matlab for ages, but my "general" approach to this in computing terms would be splitting the problem into a needle-and-haystack solution with two parts:
Create all possible search vectors from your initial search (i.e. [5 6 7 8] [6 7 8 9])
Check if any of these sub-vectors are a subset of the vector being searched.
Basically just two set-operations in a row.
You could convert your vectors to strings, and use strfind.
If x and y are your vectors:
x_str = mat2str(x);
y_str = mat2str(y);
n = strfind(x_str(2:end-1), y_str(2:end-1))
Note that you have to remove the first and last characters of the string version, as they correspond to the square brackets of the vectors.
Suppose an index vector in binary like below
Input
1 1 0 0 1 0 1
1 2 3 4 5 6 7
Intended output
1 2 5 7
which denotes nth number to be chosen. So I want to change 1 1 0 0 1 0 1 to 1 2 5 7, is there some easy way for this?
If you actually want to use your output to index another vector, do it directly.
You just need to transform your binary vector to logical
A = [1 1 0 0 1 0 1]; %assuming its double
B = [1 2 3 4 5 6 7];
C = B( logical(A) )
C =
1 2 5 7
The solution is using the function find(indicesBinary)
In Matlab I've matrix where, in a previous stage of my code, an specific element was chosen. From this point of the matrix I would like to find a maximum, not just the maximum value between all its surounding neighbours for a given radius, but the maximum value at a given angle of orientation. Let me explain this with an example:
This is matrix A:
A =
0 1 1 1 0 0 9 1 0
0 2 2 4 3 2 8 1 0
0 2 2 3 3 2 2 1 0
0 1 1 3 2 2 2 1 0
0 8 2 3 3 2 7 2 1
0 1 1 2 3 2 3 2 1
The element chosen in the first stage is the 4 in A(2,4), and the next element should be the maximum value with, for example, a 315 degrees angle of orientation, that is the 7 in A(5,7).
What I've done is, depending on the angle, subdivide matrix A in different quadrants and make a new matrix (an A's submatrix) with only the values of that quadrant.
So, for this example, the submatrix will be A's 4th quadrant:
q_A =
4 3 2 8 1 0
3 3 2 2 1 0
3 2 2 2 1 0
3 3 2 7 2 1
2 3 2 3 2 1
And now, here is my question, how can I extract the 7?
The only thing I've been able to do (and it works) is to find all the values over a threshold value and then calculate how those points are orientated. Then, saving all the values that have a similar orientation to the given one (315 degrees in this example) and finally finding the maximum among them. It works but I guess there could be a much faster and "cleaner" solution.
This is my theory, but I don't have the image processing toolbox to test it. Maybe someone who does can comment?
%make (r,c) the center by padding with zeros
if r > size(A,1)/2
At = padarray(A, [size(A,1) - r], 0, 'pre');
else
At = padarray(A, [r-1], 0 'post');
if c > size(A,2)/2
At = padarray(At, [size(A,2) - c], 0, 'pre');
else
At = padarray(At, [c-1], 0 'post');
%rotate by your angle (maybe this should be -angle or else 360-angle or 2*pi-angle, I'm not sure
Ar = imrotate(At,angle, 'nearest', 'loose'); %though I think nearest and loose are defaults
%find the max
max(Ar(size(Ar,1)/2, size(Ar,2)/2:end); %Obviously you must adjust this to handle the case of odd dimension sizes.
Also depending on your array requirements, padding with -inf might be better than 0
The following is a relatively inexpensive solution to the problem, although I found wrapping my head around the matrix coordinate system a real pain, and there is probably room to tidy it up somewhat. It simply traces all matrix entries along a line around the starting point at the supplied angle (all coordinates and angles are of course based on matrix index units):
A = [ 0 1 1 1 0 0 9 1 0
0 2 2 4 3 2 8 1 0
0 2 2 3 3 2 2 1 0
0 1 1 3 2 2 2 1 0
0 8 2 3 3 2 7 2 1
0 1 1 2 3 2 3 2 1 ];
alph = 315;
r = 2;
c = 4;
% generate a line through point (r,c) with angle alph
[nr nc] = size(A);
x = [1:0.1:nc]; % overkill
m = tan(alph);
b = r-m*c;
y = m*x + b;
crd = unique(round([y(:) x(:)]),'rows');
iok = find((crd(:,1)>0) & (crd(:,1)<=nr) & (crd(:,2)>0) & (crd(:,2)<=nc));
crd = crd(iok,:);
indx=sub2ind([nr,nc],crd(:,1),crd(:,2));
% find max and position of max
[val iv]=max(A(indx)); % <-- val is the value of the max
crd(iv,:) % <-- matrix coordinates (row, column) of max value
Result:
val =
7
iv =
8
ans =
5 7
I have a matrix lets say
x =
2 2 3
4 3 2
6 4 8
now I want to get the location of a number 4.
I want ans like this :
ans=(2,1) (3,2)
as these are the locations for 4 in matrix.
Use find:
[i,j] = find(x == 4)
ismember will return an array of 1 or 0 depending on if the cell value there is or isn't the value you're searching for:
octave:9> x
x =
2 2 3
4 3 2
6 4 8
octave:10> ismember(x,4)
ans =
0
1
0
0
0
1
0
0
0
And then you can use find and ind2sub to get the array indicies of the 1s:
octave:11> [i,j] = ind2sub(size(x),find(ismember(x,4)))
i =
2
3
j =
1
2
So that the indicies are (2,1) and (3,2).