Copy array by indexing cell numbers - matlab

Question

I am trying to extract specific columns from a "nested" array, the columns I need are nested, there are about a thousand columns, of which I only need the ones marked by index in another part of the array.
I have one Array{1,15} containing cells with numerical values (e.g. 2,5,10,53). These values are the index numbers i need to extract from another array.
indexnum = OutArray{1,15}(:);
Which arranges them in a column instead of a row, totally not necessary but seemed easier for me to progress with this.
Then I have the array containing the actual columns I want to extract/copy to a new array.
OutArray{1,14}{i,1}
So by the example numbers above, I need to copy column 2,5,10 and 53 to another array.
One of my more current attempts looks like this:
NewArray = []; %create new array
indexnum = OutArray{1,15}(:); %copy right index values to column
for i = indexnum{:} %use numeric value of every cell
NewArray = [NewArray, OutArray{1,14}{1,i}] %copy corresponding columns to NewArray
end
I also tried to use cell2mat(indexnum(1,:)), but that didn't help either.
To make clear the structure of the array:
OutArray{1,15} Contains cells with 1 value per column, which are index numbers for other array
OutArray{1,14} contains nested cells, 1 cell per column
OutArray{1,14}{1,x} contains columns with ~30 values per column, of which I want to copy the columns with the right indexes
For another array in which I just needed to copy all columns this code worked fine:
new1 = [];
for i = 1:length(OutArray{1,4})
new1 = [new1, OutArray{1,4}{i,1}]
end

Answer 1

It was a bit hard to understand because of so many cells into cells but your screenshots were very helpful. I will first highlight the errors and needed changes in your attemp:
NewArray = []; %create new array
indexnum = OutArray{1,15}(:); %copy right index values to column
for i = indexnum{:} %use numeric value of every cell
NewArray = [NewArray, OutArray{1,14}{1,i}] %copy corresponding columns to NewArray
end
Doing OutArray{1,15}(:) is exactly the same as OutArray{1,15} as you are just selecting the full cell of cells.
Your for loop uses indexnum{:} as the iterator but {:} returns a comma separated list and it does not work like (:) for arrays that give the full vector instead. In this case, when you assign indexnum{:} to a variable you get only the first element of the list. An example to ilustrate this:C = {1, 2, 3}; C{:} displays the full list, but x = C{:} only makes x = 1. To get all the elements you could group them in an array by doing: x = [C{:}].
So in your case you just need to add brackets to for i = [indexnum{:}] to get the iterator working.
To sum up, your code would be changed to:
NewArray = []; %create new array
indexnum = OutArray{1,15}; %copy right index values to column
for i = [indexnum{:}]
NewArray = [NewArray, OutArray{1,14}{1,i}}];
end
In addition, you could avoid the for loop and variables initialization with this single line code:
NewArray = [OutArray{1,14}{1,[OutArray{1,15}{1,:}]}];
As you can see, it just takes row 1 of your data OutArray{1,14} and the columns specified at each element of the indexes OutArray{1,15}. Brackets are needed twice because when indexing a cell with curly braces with more than one index at a time you always get a list and need to convert into an array as explained above.