turn a table column into doubles

Hi,

I have a Table that has a column that was read from an excel sheet. The column should be numbers but is currently shown as strings like '3.14', '2.22', .... How to turn this column into doubles?

Thanks.

jennifer

Answer 1

[Guillaume]

yourtable.columnname = str2double(yourtable.columnname);

is all that is needed.

[JFz]

Tried this but got the same error. Thanks.

[Guillaume]

You're certainly not getting the same error at all and certainly not from str2double. str2double returns NaN on invalid input, it never errors.

So:

1. What did you actually try?
2. What is the exact error you got?

[JFz]

str2double works!

[Luisana Rodriguez Sequeira]

What can we do if str2double returns NaN?

[Image Analyst]

The the column is either nans or characters or something that is not a number. So don't try to cast it to doubles then!

Answer 2

[Chaya N]

 str2num('enter your string here');

Please note that this would only work for strings that contain numerical data

[JFz]

Thanks. But my string is a table column: T.n. I keep getting error: Error using str2num (line 32) Requires string or character array input.

[Chaya N]

If your table also has other columns with numbers in them, then you would most certainly get that error message. Try passing only that particular column into your str2num() function.

Also how is this table stored? Is it a cell array or a structure?

[Guillaume]

I recommend never using str2num and using str2double instead. The latter has two advantages:

• it accepts cell arrays of string as inputs (so you can give it a whole table column as well)
• it won't format your hard drive when passed the string 'rmdir(''C:\'', ''f'')' unlike str2num (Warning! don't try! str2num will happily execute any instruction in the string)

[Chaya N]

@Guillaume: rmdir!

A bit of an extreme thing to do (even by accident), wouldn't you say?

[Guillaume]

Well, yes it's a bit extreme. The intent is to scare you.

The thing is: if you're using str2num to process any external input (from a prompt, a file, a webpage, etc.) you are asking for trouble. That input may be malicious, a prank, bad luck or invalid, str2num will not care and execute whatever instruction is in that string, with no warning.

[Chaya N]

I am learning new things here. Thank you.

[JFz]

str2double works!

Thank you so much!

Answer 3

[Image Analyst]

You could use xlsread() instead of readtable().

[JFz]

Will try it. Thanks.

Answer 4

[Priteshkumar Gohil]

e.g. if you want to convert 1st column then following should work.

yourtable.(1) = str2double(t.(1));

or

yourtable.('COLUMN_TITLE') = str2double(t.('COLUMN_TITLE'));

[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_);

[Image Analyst]

@Arshey Dhangekar, start your own question and attach the csv file and code to import it into MATLAB, presumably with the readtable() function.

[Arshey Dhangekar]

Hello I know basic thing. So only I want to know how can I convert all data into double. I attach csv file

Press=readtable ("inst0 138.221.155.184 12_10_2020 14_49_56 2.csv")
varfun(@class,Press,'OutputFormat','cell')

Output
  Columns 1 through 8

    {'double'}    {'cell'}    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}

  Columns 9 through 16

    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}    {'double'}

  Columns 17 through 25

    {'double'}    {'double'}    {'cell'}    {'cell'}    {'cell'}    {'cell'}    {'cell'}    {'cell'}    {'cell'}

  Columns 26 through 29

    {'cell'}    {'cell'}    {'cell'}    {'double'}