check if ALL elements of a vector are in another vector - arrays

I need to loop through coloumn 1 of a matrix and return (i) when I have come across ALL of the elements of another vector which i can predefine.
check_vector = [1:43] %% I dont actually need to predefine this - i know I am looking for the numbers 1 to 43.
matrix_a coloumn 1 (which is the only coloumn i am interested in looks like this for example
1
4
3
5
6
7
8
9
10
11
12
13
14
16
15
18
17
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
1
3
4
2
6
7
8
We want to loop through matrix_a and return the value of (i) when we have hit all of the numbers in the range 1 to 43.
In the above example we are looking for all the numbers from 1 to 43 and the iteration will end round about position 47 in matrix_a because it is at this point that we hit number '2' which is the last number to complete all numbers in the sequence 1 to 43.
It doesnt matter if we hit several of one number on the way, we count all those - we just want to know when we have reached all the numbers from the check vector or in this example in the sequence 1 to 43.
Ive tried something like:
completed = []
for i = 1:43
complete(i) = find(matrix_a(:,1) == i,1,'first')
end
but not working.

Assuming A as the input column vector, two approaches could be suggested here.
Approach #1
With arrayfun -
check_vector = [1:43]
idx = find(arrayfun(#(n) all(ismember(check_vector,A(1:n))),1:numel(A)),1)+1
gives -
idx =
47
Approach #2
With customary bsxfun -
check_vector = [1:43]
idx = find(all(cumsum(bsxfun(#eq,A(:),check_vector),1)~=0,2),1)+1

To find the first entry at which all unique values of matrix_a have already appeared (that is, if check_vector consists of all unique values of matrix_a): the unique function almost gives the answer:
[~, ind] = unique(matrix_a, 'first');
result = max(ind);

Someone might have a more compact answer but is this what your after?
maxIndex = 0;
for ii=1:length(a)
[f,index] = ismember(ii,a);
maxIndex=max(maxIndex,max(index));
end
maxIndex

Here is one solution without a loop and without any conditions on the vectors to be compared. Given two vectors a and b, this code will find the smallest index idx where a(1:idx) contains all elements of b. idx will be 0 when b is not contained in a.
a = [ 1 4 3 5 6 7 8 9 10 11 12 13 14 16 15 18 17 19 20 21 22 23 24 25 26 ...
27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 1 3 4 2 6 7 8 50];
b = 1:43;
[~, Loca] = ismember(b,a);
idx = max(Loca) * all(Loca);
Some details:
ismember(b,a) checks if all elements of b can be found in a and the output Loca lists the indices of these elements within a. The index will be 0, if the element cannot be found in a.
idx = max(Loca) then is the highest index in this list of indices, so the smallest one where all elements of b are found within a(1:idx).
all(Loca) finally checks if all indices in Loca are nonzero, i.e. if all elements of b have been found in a.

Related

How to find the size of smallest and largest bin in MATLAB?

I need to find the the size of bin with maximum and minimum element. I am using histc function in MATLAB.
Here is what I am doing,
A=[1 2 3 11 22 3 4 55 6 7 2 33 44 5 22]
edges = [10 inf];
N = histc(A,edges)
it gives N=[6,0]; means there are 6 elements having values greater than 10. Now I want to count what is the maximum count in a bin for my condition.
here it should be 2 as there are two instances where we have two integers satisfying my condition 11 22 and 33 44
How to count it in MATLAB.
Here you go;
A=[1 2 3 11 22 3 4 55 6 7 2 33 44 5 22]
arr=diff([0 (find(~(A>10))) numel(A)+1]) -1;
arr(find(arr(1,:)==0))=[];
largest=max(arr); % longest sequence of occurences of numbers > 10
smallest=min(arr); % smallest sequence of occurences of numbers > 10
Cheers!!

Matlab: reshape 3-dimensional array into 2-dimensional array

I have a 3x3x2000 array of rotation matrices that I need to transform into a 2000x9 array.
I think I have to use a combination of permute() and reshape(), but I don't get the correct output order.
This is what I need:
First row of 3x3 array needs to be columns 1:3 in the output
Second row of 3x3 array needs to be columns 4:6 in the output
Third row of 3x3 array needs to be columns 7:9 in the output
I have tried all possible combinations of numbers 1 2 3 in the following code:
out1 = permute(input, [2 3 1]);
out2 = reshape(out1, [2000 9]);
But I always end up with the wrong order. Any tips for a Matlab newbie?
How about a simple for-loop?
for i=1:size(myinput,3)
myoutput(i,:)=[myinput(1,:,i) myinput(2,:,i) myinput(3,:,i)];
% or
% myoutput(i,:)=reshape(myinput(:,:,i),[],9);
end
It's not simple as using permute and reshape, but it is transparent and easier for debugging. Once everything in your program runs perfectly, you can consider to rewrite such for-loops in your code...
You had a mix-up in your permute
a = reshape(1:9*6, 3, 3, []);
a is a 3x3x6 matrix, each
a(:,:,i) = 9*(i-1) + [1 4 7
2 5 8
3 6 9];
So
out1 = permute(a, [3,1,2]);
out2 = reshape(out1, [], 9);
Or in one line
out3 = reshape(permute(a, [3,1,2]), [], 9);
So
out2 = out3 =
1 2 3 4 5 6 7 8 9
10 11 12 13 14 15 16 17 18
19 20 21 22 23 24 25 26 27
28 29 30 31 32 33 34 35 36
37 38 39 40 41 42 43 44 45
46 47 48 49 50 51 52 53 54

Retrieving specific elements in matlab from arrays in MATLAB

I have an array in MATLAB
For example
a = 1:100;
I want to select the first 4 element in every successive 10 elements.
In this example I want to b will be
b = [1,2,3,4,11,12,13,14, ...]
can I do it without for loop?
I read in the internet that i can select the element for each step:
b = a(1:10:end);
but this is not working for me.
Can you help me?
With reshape
%// reshaping your matrix to nx10 so that it has successive 10 elements in each row
temp = reshape(a,10,[]).'; %//'
%// taking first 4 columns and reshaping them back to a row vector
b = reshape(temp(:,1:4).',1,[]); %//'
Sample Run for smaller size (although this works for your actual dimensions)
a = 1:20;
>> b
b =
1 2 3 4 11 12 13 14
To vectorize the operation you must generate the indices you wish to extract:
a = 1:100;
b = a(reshape(bsxfun(#plus,(1:4)',0:10:length(a)-1),[],1));
Let's break down how this works. First, the bsxfun function. This performs a function, here it is addition (#plus) on each element of a vector. Since you want elements 1:4 we make this one dimension and the other dimension increases by tens. this will lead a Nx4 matrix where N is the number of groups of 4 we wish to extract.
The reshape function simply vectorizes this matrix so that we can use it to index the vector a. To better understand this line, try taking a look at the output of each function.
Sample Output:
>> b = a(reshape(bsxfun(#plus,(1:4)',0:10:length(a)-1),[],1))
b =
Columns 1 through 19
1 2 3 4 11 12 13 14 21 22 23 24 31 32 33 34 41 42 43
Columns 20 through 38
44 51 52 53 54 61 62 63 64 71 72 73 74 81 82 83 84 91 92
Columns 39 through 40
93 94

Matlab - replicating arrays values according to occurrences array

For example, A = [19 20 21 22 23 24 25]; B = [2 0 3 0 0 0 2];
How can we get a new array, repeating each value from B accordingly X times?
For example, answer here is: [19 19 21 21 21 25 25].
Please note that I am only allowed to a for loop combined with a repmat call.
If you are only allowed to use repmat and a for loop, you can do the following:
S = [];
for idx = 1 : length(B)
S = [S repmat(A(idx), 1, B(idx))];
end
S is initially a blank array, then for as many values as there are in B (or A since they're both equal in length), simply concatenate S with each value in A that is repeated by the corresponding number in B. S will contain the output.
By running the above example, I get:
S =
19 19 21 21 21 25 25
However, I highly recommend you use more vectorized approaches. I'll leave that to you as an exercise.
Good luck!

Vectorized range checking in Matlab

In trying to port an algorithm from C# to Matlab I found that Matlab is inefficient at running for loops. As such I want to vectorize the algorithm.
I have following inputs:
lowrange:
[ 00 10 20 30 40 50 ... ]
highrange:
[ 10 20 30 40 50 60 ... ]
These arrays are equal in length.
I now have a third array Values (which could be any length) and for this array I want to count the occurrences of Values elements between lowerange(i) and highrange(i) (You can see I'm coming from a for loop).
The output should be an array of length lowrange/highrange.
So with the above arrays and input LineData:
[ 1 2 3 4 6 11 12 16 31 34 45 ]
I expect to get:
[ 05 03 00 02 01 00 ... ]
I tried the (for me) obvious thing:
LineData(LineData < PixelEnd & LineData > PixelStart)
But that doesn't work because it just checks LineData on an element by element way. It does not try to apply the comparison over all values in LineData.
Unfortunately, I cannot come up with anything else since I'm not yet used to think in a Matlab 'vector' way, let alone knowing all applicable instructions from memory.
As you are looking to do a basic histogram with given edges, you can use Matlabs built-in function histc:
values = [ 1 2 3 4 6 11 12 16 31 34 45 ];
edges = 0:10:60;
histc(values, edges)
ans =
5 3 0 2 1 0 0
For ranges with identical intervals and starting from 0, here's a bsxfun based counting approach -
LineData = [ 1 2 3 4 6 11 12 16 31 34 45 ] %// Input
interval = 10; %// interval width
num_itervals = 6; %// number of intervals
%// Get matches for each interval and sum them within each interval for the counts
out = sum(bsxfun(#eq,ceil(LineData(:)/interval),1:num_itervals))
Output -
LineData =
1 2 3 4 6 11 12 16 31 34 45
out =
5 3 0 2 1 0
Assuming that the last interval would be the one holding the max of input data, you can try out a diff + indexing based approach too -
LineData = [ 1 2 3 4 6 11 12 16 31 34 45 ] %// Input
interval = 10; %// interval width
labels = ceil(LineData(:)/interval); %// set labels to each input entry
df_labels = diff(labels)~=0; %// mark the change of labels
df_labels_pos = find([df_labels; 1]); %// get the positions of label change
intv_pos= labels([true;df_labels]);%// position of each interval with nonzero counts
%// get counts from interval between label position change and put at right places
out(intv_pos) = [ df_labels_pos(1) ; diff(df_labels_pos)];

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