Error with the division

Hello everyone,

load('DATI_MAR_ANNUALI'); 
load('DATA_ECM');
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!

[Steven Lord]

What is the full and exact text (everything displayed in red and/or orange in the Command Window) of the error and/or warning messages you receive when you run your code? The exact text of the messages may include information that will help us determine the problem or at least the next step to take in investigating the problem.

[Mathieu NOE]

hello (again !)

a and b are tables - you cannot do directly

c=(a-b)./a

d=c*100

you can do it f you select elements from the tables

[Pul]

@Mathieu NOE Can I convert tables into something that allows me to use that operator?

@Steven Lord This is the error: "Operator '-' is not supported for operands of type 'table'."

[Mathieu NOE]

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]

Exactly, but I solved the problem. Thank you!

Answer 1

[Star Strider]

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]

Okay, got it. I solved it.

Thank you!

[Star Strider]

As always, my pleasure!

.

Answer 2

[Peter Perkins]

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]

Yes, got it, thank you!