How to sort a table within groups

Hi all,

I have a table with variables 'Date', 'ID', Price', 'Volumn', all with daily value. The 'Date' repeats itself. Now I want to first group the table based on 'Date', and within each group (namely each date), I want to sort the table according to 'Price', from high to low. I know varfun can help me gruop the table and do the sorting, but the output will not contain 'ID' and 'Volumn'. I still want to researve the other variables. What shall I do?

Many thanks.

Answer 1

[Adam Danz]

sortrows()

Examples

[Elbert Liu]

Thank you! It works!

Answer 2

[Guillaume]

I don't think you can use varfun for this. This is how I'd do it:

group = findgroups(yourtable.Date);
ordering = cell2mat(splitapply(@(x) {sortrows(x)}, [yourtable.Price, (1:height(yourtable))'], group));
sortedtable = yourtable(ordering(:, 2));

The trick here is to sort by price in each group but keep track of the original row (ordering(:, 2)) from the whole table, then reorder according to that.

[Yean Lim]

Hi, I tried to run

sortedtable = yourtable(ordering(:, 2));

However, I got an error message saying:

Subscripting into a table using one subscript (as in t(i)) or three or more subscripts (as in t(i,j,k)) is not
supported. Always specify a row subscript and a variable subscript, as in t(rows,vars). 

Please advise how to fix this error. Thanks

[Ecco]

As I found the answer today and helpful:

There is a ",:" missing:

sortedtable = yourtable(ordering(:, 2),:);