How to break a large table into a set of smaller tables?

Hi,

I have a very large table (priceTbl) of 4 columns. I want to break the large table into a set of smaller tables such that each small table has the same value in column 2 and 4.

How to do that?

Thanks,

Jen

Answer 1

[Peter Perkins]

Jennifer, it's hard to answer this question without knowing whether "table" means "the MATLAB table data type" or something else, and without knowing what is in the table. Walter's suggestion assumes a table as in "the data type", and further, that variables 2 and 4 in that table are valid inputs to unique(...,'rows'). (Walter, Gold Star for writing working code despite apparently not being able to run it, although you actually only need 13b or later to use tables.) Given that, here's a (perhaps) slightly more direct version of Walter's code:

[~,~,i] = unique(BigTable(:,[2 4]));
for k = 1 : max(i)
  TableCell{k} = BigTable(i == k,:);
end

If you're into the whole brevity thing, rowfun lets you do it without a loop:

rowfun(@(x1,x2,x3,x4) table(x1,x2,x3,x4),BigTable, ...
       'InputVariables',1:4,'GroupingVariables',[2 4], ...
       'OutputFormat','cell')

But Jennifer, given the warning and error that you're getting, it seems likely that either you don't have a table, or the table contains something unusual in those variables. You'll have to provide a short example of your data.

[JFz]

Thank you!

Here, table means Matlab table data type. I will give an example, but first I need to make it generic.

Jennifer

Answer 2

[Walter Roberson]

col24 = BigTable{:,[2 4]};
u24 = unique(col24, 'rows');
numentry = size(u24,1);
TableCell = cell(numentry,1);
for K = 1 : numentry
  insubset = BigTable{:,2} == u24(K,1) && BigTable{:,4} == u24(K,2);
  TableCell{K} = BigTable(insubset,:);
end

[Image Analyst]

Aren't those cell arrays when she asked about tables ?

[Walter Roberson]

When you index a table with () you get a table as a result. When you index a table with {} you get the contents of the rows or columns as the result. See http://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

[JFz]

Thank you so much, Walter! Really appreciate it. But when I tried it, the 2nd line gives me the error:

>> u24 = unique(col24, 'rows'); Warning: The 'rows' input is not supported for cell array inputs. > In cell.unique>celluniqueR2012a at 236 In cell.unique at 148

Do you know what is the problem here?

Also, I got this error: Undefined function 'eq' for input arguments of type 'cell'.

when trying:

insubset = BigTable{:,2} == u24(K,1) && BigTable{:,4} == u24(K,2);

Again, thanks. Really appreciate it. Jennifer

[Walter Roberson]

Unfortunately I do not have R2014b or later and so cannot test any code that contains tables.