MATLAB: Grouped difference between two tables

grouping variablesMATLABtables

Is there a slick way to apply a function (in my case find the difference) between two tables if they have the same variable names in both tables but different numbers of rows. in my case I have one table of average values generated by varfun using a grouping variable and I want to subtract the values in that table from the second table for all other variables when the grouping variable matches between the two tables. I can easily loop through it and get it that way or create index groups by row, but as I have not used tables a whole lot, I am hoping there is a neat/efficient way that I have not thought of.

thanks

Best Answer

What I ended up doing, as I know the table columns and order for both tables, was to use an outer join and then split the table into two, subtracting one from the other. it worked quite well.

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MATLAB: Cells merging in table

varfun(@(c) {vertcat(c{:})}, table1, 'GroupingVariables', 'Var1', 'InputVariables', 5:width(table1))

varfun(@(c) {vertcat(c{:})}, table1, 'GroupingVariables', {'Var1', 'Var2'}, 'InputVariables', 5:width(table1))

varfun(@(c) {vertcat(c{:})}, table1, 'GroupingVariables', {'Var1', 'Var2', 'Var3'}, 'InputVariables', 5:width(table1))

MATLAB: Existing table, populate a column with string (receiving errors)

You are close, but you are trying to assign a character vector to a double variable (NaN = not a number). You can see that if you run the command summary(mytable).

You also do not need to put the text into a cell if you use the string data type.

See if you can get this code to work for your needs.

myArray = nan(5,2)
mytable = array2table(myArray);
mytable.Properties.VariableNames = {'colA', 'colB'};
mytable2 = convertvars(mytable,"colB",'string');
mytable2.colA(:) = 459;
mytable2.colB(:) = "words"

You say you have a lot of data. If the variables already exist, you could do something like this:

colA = nan(5,1);
colB = strings(5,1);
mytable = table(colA,colB);
mytable.colA(:) = 459; % just a random number, proof-of-concept that it works
mytable.colB(:) = "words" % this throws errors

Best Answer

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MATLAB: Cells merging in table

MATLAB: Existing table, populate a column with string (receiving errors)

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