# Error with the division

5 views (last 30 days)
Pul on 25 Nov 2021
Commented: Star Strider on 30 Nov 2021
Hello everyone,
a=DATIMARannuali;
b=DATIECMWFannuali;
c=(a-b)./a
d=c*100
this is my code, but I get an error trying to do the division; how can I solve it?
Thank you!
Mathieu NOE on 26 Nov 2021
hello @Pul
can you explain what is the intention ? the tables contain multiple columns so the math you want to do is for which ones ?
Pul on 30 Nov 2021
Exactly, but I solved the problem. Thank you!

Star Strider on 26 Nov 2021
Use the table2array function to convert the contents of the table to an array. Assign the arrays to new variables rather than over-writing the tables, since the references in the tables may be useful later in the code.
However the first column of the (40x13) table ‘DATIMARannuali’ is a year value (not a datetime array) with the variable name 'Year' so including that in the calculation may not be appropriate. While I did not download and open ‘DATA_ECM.mat’ the sizes of the two tables must match for tthe element-wise calculations to succeed, and the variables must be the same (or have similar contexts) for the calculation to make any sense.
.
Pul on 30 Nov 2021
Okay, got it. I solved it.
Thank you!
Star Strider on 30 Nov 2021
As always, my pleasure!
.

Peter Perkins on 26 Nov 2021
As StarStride hints, these tables are not even the same size, in either dimension:
>> DATIECMWFannuali
DATIECMWFannuali =
24×17 table
[snip]
>> DATIMARannuali
DATIMARannuali =
40×13 table
[snip]
If they were, there are a few ways to do this, all more or less syntactic variations on the same thing: a table is a container, and you need to do the math on the contents, not the container. As SS points out, one of the variables in these tables is a year number, and surely you dont want to include that in the calculation. So first, probably, convert to timetables.
Given that, the simplest thing would be something like
c = (DATIECMWFannuali.Variables-DATIMARannuali.Variables)./DATIECMWFannuali.Variables;
d = array2table(c*100,'VariableNames',DATIECMWFannuali.Properties.VariableNames);
or perhaps
a = DATIECMWFannuali.Variables; % or DATIECMWFannuali{:,:}, or table2array(DATIECMWFannuali)
b = DATIMARannuali.Variables; % or ...
c = (b-a)./a;
d = array2table(c*100,'VariableNames',DATIECMWFannuali.Properties.VariableNames);
If you leave them as tables, then probably the ...{:,:} syntax is easiest, because you can use ...{:,2:end}.
The whole topic of "doing math on data in tables" is explored here: "This example ... shows how to perform calculations by using the numeric and categorical data that the table contains." You might find that helpful.
Pul on 30 Nov 2021
Yes, got it, thank you!