how to make a colum of multiple 1 to 5. i want to make column vector of [1;1;1;1;1​;1;1;1;1;1​;1;1;1;1;2​;2;2;2;2;2​;2;2;2;2;2​;2;2;2;3;3​;3;3;3;3;3​;3;3;3;3;3​;3]. is there any way to make this kind of vector instead of typing this many times.

i want to print [1;1;1;1;1;1;1;1;1;1;1;1;1;;1;1;1;1;1;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;2;3;3;3;3;;33;3]. but without typing numbers all the time. how to print 14 times 1, 20 times 2, 50 times 3 in one column vector.

[Jan]

Is this a homework question?

[Pooja Patel]

Dear Jan Simon this is not actually a homework question. its a part of my project. thank you

Answer 1

[John BG]

even easier

A=[ones(1,1) 2*ones(1,20) 3*ones(1,50)]'

if you find this answer useful would you please be so kind to mark my answer as Accepted Answer?

To any other reader, please if you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

[Guillaume]

Well, it is assumed that the question is how to generate repeats of a column vector of arbitrary length given a repeat vector of the same length. Your code is not easily extendable to:

vectortorepeat = randi(50, 200, 1);
repeatcounts = randi(20, 200, 1);

[Pooja Patel]

Thank you Mr. John BG. This is working very well.

[John BG]

Pooja

thanks very much for accepting my answer, sometimes the simplest solution is the best solution

:)

regards

John BG

<mailto:[e-mail] [e-mail]>

Answer 2

[Guillaume]

repelem([1;2;3], [14, 20, 50])

[Pooja Patel]

Dear Guillaume, thank you so much for your response. I am using Matlab14. it is showing this error "Undefined function 'repelem' for input arguments of type 'double'." so please help me through this.

[Guillaume]

You can define repelem with:

repelem = @(rowv, reps) cell2mat(arrayfun(@(rowv, reps) repmat(colv, reps, 1), colv, reps, 'UniformOutput', false));

And call it with

repelem([1;2;3], [14;20;50]) %BOTH inputs MUST be column vectors

Note that the above is not a generic replacement for repelem, but one that will work for your case.

[Pooja Patel]

This is done with using repmat function. [repmat([1],14,1); repmat([2],20,1)] Thank you

Answer 3

[Jan]

Then use https://www.mathworks.com/matlabcentral/fileexchange/41813-runlength:

RunLength([1;2;3], [14, 20, 50])

Or:

B = [1, 2, 3];
N = [14, 20, 50];

Accum  = cumsum([1, N]);
Index  = zeros(1, sum(N));
Index(Accum(1:end - 1)) = 1;
Index  = cumsum(Index);
Result = B(Index);

The idea is to create an index vector, which is as long as the output and contains a 1 on every position of a new value. Then after cumsum-ming this vector contains the index related to the input values repeated N times.

If you are in doubt about such smart indexing tricks, create a simple loop:

C = cell(1, numel(B));
for iC = 1:numel(B)
  C{iC} = repmat(B(ic), N(iC), 1);
end
Result = cat(1, C{:});

Now the parts are created one after the other and stored in a cell. Finally all parts are concatenated. This is not very efficient, but perhaps you do not want to do this millions of times.

[Pooja Patel]

Thank you Mr.Jan Simon. this is helpful.

[Pooja Patel]

Error using RunLength (line 70) Compilation failed.

but second one the cumcum one and repmat one are working very well. thank you so much for your support

Answer 4

[John BG]

thanks Guillame for pointing that out

Hi Pooja Patel

even easier

1. for the data given in the question

A=[ones(1,1) 2*ones(1,20) 3*ones(1,50)]'

or for any data, modify or replace the randi lines accordingly

V=[]
vc=randi([-10 10],5,1) % repeat this
repc=randi([2 10],5,1) % n times each

for k=1:1:length(vc)
V=[V ;vc(k)*ones(repc(k),1)];
end
V(1)=[]

if you find this answer useful would you please be so kind to mark my answer as Accepted Answer?

To any other reader, please if you find this answer of any help solving your question,

please click on the thumbs-up vote link,

thanks in advance

John BG

<mailto:[e-mail] [e-mail]>

[Jan]

V(1)=[] is a typo. There is no reason to delete the first element of the output.

Letting an array grow iteratively is extremely inefficient. The costs grow exponentially and therefore the editor shows the MLint warning in the line "V = [V; ...]":

 The variable 'V' appears to change size on every loop iteration.
 Consider preallocating for speed.

Pre-allocation is the first rule to be considered for writing efficient Matlab code.

Try it:

function myTest
B = (1:4000).';
N = repmat(20, size(B));

tic
for k = 1:10
  V = test1(B, N);
end
toc

tic
for k = 1:10
  V = test2(B, N);
end
toc

function V = test1(B, N)
V = [];
for k=1:1:length(N)
    V=[V ;B(k)*ones(N(k),1)];
end

function V = test2(B, N)
Accum  = cumsum([1; N(:)]);
Index  = zeros(1, sum(N));
Index(Accum(1:end - 1)) = 1;
Index  = cumsum(Index);
V      = B(Index);

 >> Elapsed time is 2.164152 seconds.   % Iterative growing
 >> Elapsed time is 0.009183 seconds.   % Logical indexing

And exponential growing means, that for an input with the double size, the code needs much more than the double size. For 8000 elements:

Elapsed time is 11.990776 seconds.   % Iterative growing
Elapsed time is  0.026229 seconds.   % Logical indexing

Answer 5

[Pooja Patel]

this is done by using repmat function. [repmat([1],14,1); repmat([2],20,1)] Thank you