How to do math to entirety of a vector?

selectIndicies = [selectSpaces:-1:selectSpaces-6]

I have this line that is supposed takes a vector of N columns (selectspaces) and gives me the number of selectSpaces and the 6 numbers before it.

For example, if selectSpaces was [7 21] then i would like to get the vector [1 2 3 4 5 6 7 15 16 17 18 19 20 21], but right now all i get is [1 2 3 4 5 6 7].

How can i do this without loops?

Thanks!

Answer 1

[Star Strider]

Creating it as an anonymolus function and using it with arrayfun and cell2mat is an option —

selectIndicies = @(selectSpaces) [selectSpaces:-1:selectSpaces-6];

desiredResult = cell2mat(arrayfun(selectIndicies,[7 21], 'Unif',0))

desiredResult = 1×14

7 6 5 4 3 2 1 21 20 19 18 17 16 15

desiredResult = cell2mat(arrayfun(selectIndicies,[7 21 63], 'Unif',0))

desiredResult = 1×21

7 6 5 4 3 2 1 21 20 19 18 17 16 15 63 62 61 60 59 58 57

.

[Xavier Bardwell]

Is there any way to make it so that instead of [7 6 5 4 3 2 1...] its [1 2 3 4 5 6 7]?

[Star Strider]

That would simply require changing the subscript references:

selectIndicies = @(selectSpaces) [selectSpaces-6:selectSpaces];

desiredResult = cell2mat(arrayfun(selectIndicies,[7 21], 'Unif',0))

desiredResult = 1×14

1 2 3 4 5 6 7 15 16 17 18 19 20 21

desiredResult = cell2mat(arrayfun(selectIndicies,[7 21 63], 'Unif',0))

desiredResult = 1×21

1 2 3 4 5 6 7 15 16 17 18 19 20 21 57 58 59 60 61 62 63

Ideally, this would need to incorporate logic to prevent non-positive indices:

selectIndicies = @(selectSpaces) [selectSpaces-6:selectSpaces].*(selectSpaces > 6)+ones(size(selectSpaces)).*(selectSpaces<6);
desiredResult = cell2mat(arrayfun(selectIndicies,[4 7 21], 'Unif',0))

desiredResult = 1×21

1 1 1 1 1 1 1 1 2 3 4 5 6 7 15 16 17 18 19 20 21

So in this instance, if an argument were less than 7, the result would simply be a series of 1 signalling an inappropriate argument and preventing a subscript error. There are likely other ways to correct for out-of-range arguments, and producing different results. This is just one example.

Experiment to get the result you want.

.

[Stephen23]

Note that the square brackets are not required, to group use parentheses (exactly as MATLAB mlint recommends).

Answer 2

[David Hill]

[1:selectSpaces(1),diff(selectSpaces)+1:selectSpaces(2)];

[Xavier Bardwell]

Thank you! But, it is not always a 2 column vector. Is there any way to do it for infintely many numbers?

[Xavier Bardwell]

And the first number is not always 7

[David Hill]

a=[8,26,46,100];
b=a-6;
Out=[];
for k=1:numel(a)
  Out=[Out,b(k):a(k)];
end