Is there a better way to use cellfun with arguments? and is it better than for-loop?

Hey,

When I use cellfun, with a function that has arguments, I use repmat function to duplicate my arguments. My question is, if there is a better way to do this.

Here is an example

Lets say that I have a cell array of matricies and I want to get the size of dimention 1 in each

%Create a cell array with random values
randVal = @(x) magic(randi(5,2))
cellArr = arrayfun(randVal, ones(10,1),'uniformOutput',false);

%Get the size of the first dimention of each element in the cell aray
sizes = cellfun(@size,cellArr,repmat({1},size(cellArr,1),1));

This is the part that I am asking about:

repmat({1},size(cellArr,1),1)

Is there a better way to do this?

And in general, is this better that using a for-loop ?

[Rik]

How is what you want different from what Steven posted in his answer? It seems to me that is what you need. Using an anonymous function is a better way than replicating data.

[ytzhak goussha]

I stand corrected. You are right!

You were right @Rikk, @Steven Lord' s post was right on the mark and I just didn't understand it.

I removed my comment.

Again, thank you all

Answer 1

[Jan]

sizes = cellfun('size', cellArr, 1);

Using the CHAR vector arguments is mentioned in the documentation as "backward compatibility". This calling style is the only one, in which cellfun is faster than a simple loop.

[Rik]

+1

One minor addition: you need to be careful when using this syntax. Not everything works as expected, even for the fundamental classes. For more details, you may want to read this.

[ytzhak goussha]

Thank you for your comment and answer,

Though I often use the size function in a cellfun, I used it here only for the example.

In my code, I use a different custom function.

So if I understand correctly,

1. There is no workaround the whole "repmat" function
2. Unless my code explicitly demands that I use cellfun, there is no real good reason to use it.

[Rik]

It looks like this should be possible, but your example is too contrived for me to see if this is what you mean:

arg2=1;
cellfun(@(arg1)size(arg1,arg2),cellArr);

I suspect this is what you need, but with size as the example it is hard to tell.

[Jan]

Rik's argument is important: If the cell contains e.g. strings, the 'size' command (as char vector) will fail.

I prefer loops. cellfun, arrayfun, structfun allow very compact code. But usually they are harder to read and to maintain. I like fast code also, but I've seen to many projects failing due to a too complex design which impedes the debugging. Therefore is prefer dull loops. The KISS style...

Answer 2

[Steven Lord]

A = {1:10, magic(5), @sin}

A = 1×3 cell array
    {[1 2 3 4 5 6 7 8 9 10]}    {5×5 double}    {@sin}

cellfun(@(x) size(x, 1), A)

ans = 1×3

1 5 1

[ytzhak goussha]

Thank you @Steven Lord, this is great.