How to pre-allocate table rows

What is the clean way to preallocate rows in a table?

Here is an example to illustrate what I would like:

a = {'a'}
b = 1
a = table( a, b )
a(10,:) = %Some placeholder value to ensure table is extended to be 10 rows

In the example above, the table is trivial, so I could write out the following line. But since the types are known, then MATLAB could in theory just fill this in by itself.

a(10,:) = {{[]}, 0}

Answer 1

[Peter Perkins]

Danial, I interpret your question as

"I have a table with one row. I'd need the same table, but lengthened to 10 rows so that I can fill in rows 2-9 without growing it one row at a time."

This actually isn't specific to table, although the fact that tables can hold heterogeneous types makes it a bit more interesting.

(By the way, good on you for knowing to start with {'a'}, and not just 'a'.)

One option is to simply repmat the one-row table to be 10 rows:

>> t = table({'a'},1)
t = 
    Var1    Var2
    ____    ____
    'a'     1   
>> t = repmat(t,10,1)
t = 
    Var1    Var2
    ____    ____
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1   
    'a'     1

If you're filling in the table, it doesn't much matter what's in rows 2-9, since you'll be overwriting them. But if you're a stickler, you can assign to the 11'th row, then delete it:

>> t = table({'a'},1);
>> t(11,:) = t(1,:);
>> t(11,:) = []
t = 
    Var1    Var2
    ____    ____
    'a'     1   
    []      0   
    []      0   
    []      0   
    []      0   
    []      0   
    []      0   
    []      0   
    []      0   
    []      0

Hope this helps.

[Daniel Armyr]

Your second answer is brilliant. One a one-liner, but close enough.

Answer 2

[Subhadra Mahanti]

I can think of several ways to do it depending on your data. One way would be: create a cell array of row x column and covert that to a table

data=cell(5,3);
myTable = cell2table(data);
% You can alwayschange the variable names of the table later
myTable.Properties.VariableNames = {'Col1', 'Col2', 'Col3'};
myTable.Properties.RowNames = {'Row1', 'Row2', 'Row3','Row4','Row5'};