How do I convert table data to double to manipulate them?

I extract data from a table. When I retrieve an element, it is in table format, but I encounter an error when attempting to perform operations like multiplication. Is there a direct command or a series of steps to address this issue?

[Jan]

Please post any details: An example input, the code you use and the complete error message. Then writing an answer requires less guessing, what you are doing.

[Stephen23]

"I extracted data from a table, when I get an element it comes as table format but when trying to make some operations like multiplication there is an error, is there any direct command or a series of steps?"

You could use TABLE2ARRAY, but by far the simplest and most efficient approach is to just use the correct indexing using curly braces to access the table content (not parentheses which returns another table, which is what you did).

The different types of indexing are clearly explained in the documentation:

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

[Peter Perkins]

This new example goes even further into indexing and the topic of "doing math on data stored in a MATLAB table":

https://www.mathworks.com/help/matlab/matlab_prog/computations-with-numeric-data-in-table-or-timetable.html

It's a new-for-R2021b example, but doesn't require the latest MATLAB for anything (most anything?) it covers.

Answer 1

[Star Strider]

There are several ways you can convert or extract table data to an array. 

You can use dot notation or curly brace indexing, as described in the following documentation:

Access Data in Tables

https://www.mathworks.com/help/matlab/matlab_prog/access-data-in-a-table.html

A = T.Variables% All table data concatenated into an array 
A = T{:,:}% All table data concatenated into an array 
A = T{rows,vars}% Specified rows and variables into an array 

You can also use the "table2array" function. 

A = table2array(T) 

And finally, there are many operations you can perform on table data without converting it at all. For examples, see the following documentation:

Direct Calculations on Tables and Timetables

https://www.mathworks.com/help/matlab/matlab_prog/direct-calculations-on-tables-and-timetables.html

Calculations When Tables Have Both Numeric and Nonnumeric Data

https://www.mathworks.com/help/matlab/matlab_prog/calculations-when-tables-have-both-numeric-and-nonnumeric-data.html

[Al in St. Louis]

table2array worked for me. Thanks!

[Star Strider]

My pleasure!

[Ivania Jimenez-Lara]

would you mind showing me what the code for that would look like?

[Adish]

awesome

[Peter Perkins]

In recent versions of MATLAB, tables and timetables support many element+wise and reduction math operations:

t1 = table([1;2;3],[4;5;6]);
sum(t1,1)

ans = 1×2 table
    Var1    Var2
    ____    ____

     6       15 

t2 = table([7;8;9],[10;11;12]);
t1 + t2

ans = 3×2 table
    Var1    Var2
    ____    ____

      8      14 
     10      16 
     12      18 

For many other operations, see https://www.mathworks.com/help/matlab/matlab_prog/computations-with-numeric-data-in-table-or-timetable.html.

Answer 2

[Peter Perkins]

The answer might be as simple as something like T.Z = T.x .* T.y. Without more information, hard to tell.

Answer 3

[Roger Breton]

It does not work for me : all I want is to be able to import a range from Excel, and all I get is a "Table" on which I can't do any operation?

[Peter Perkins]

Tables are containers for mixed-type data, which is why they don't support "math". You haven't said anything about what you have in the spreadsheet or what you want to do with it. Maybe all your data are all numeric. The syntax I suggested might be what you are looking for to do your operation, or maybe you want to use table2array as SS suggested. Hard to say with no information.

[Roger Breton]

Thank you so much for extending your kind help, Peter.

Yes, all my data is numieric, doubles, in fact. It's just that I'm totally "green" with regards to MatLab data types. I think I used the table2array function to "convert" the data. Once converted, I was able to carry my "normal" arithmetic operation. I really have to give myself the time to learn Matlab...

[Stephen23]

If you just need a numeric matrix, why are you importing the data as a table? Use READMATRIX instead.

Answer 4

[Arshey Dhangekar]

Hello I have csv data of 18 columns and want to convert into double

so instead of writing 18 str2double code how can I convert all the 18 columns in short line of code

Temp.x310_Ambient__C_ = str2double (Temp.x310_Ambient__C_);

[Peter Perkins]

1) Post a new question, don't ask a question in a reply to someone else's question.

2) Try varfun or convertvars.

3) Get to the root cause and figure out why your numeric spreadsheet is being read in as text.

[Mohsin Munir]

I have data in excel. there are some coulmns having inputs. I want if i multiply two columns in matlab then the next column to be added in the same sheet rather than a new file in workspace. can anybody help me in this problem

[Peter Perkins]

1) Post a new question, don't ask a question in a reply to someone else's question.

2) This example may be of help for the topic of "doing math on data stored in a MATLAB table":

https://www.mathworks.com/help/matlab/matlab_prog/computations-with-numeric-data-in-table-or-timetable.html

It's a new-for-R2021b example, but doesn't require the latest MATLAB for anything (most anything?) it covers.