Error using plot Invalid data argument (Data from Excel)

Hello,

I'm having a problem as I try to plot two columns of data from excel (temperature over time). I keep getting the following error. (Error using plot

Invalid data argument.) My code is below.

%%Use readtable for importing data from excel%%
WData = readtable('WeatherData1.xlsx');

%(1)Determine Temperature Variations throughout the year.
%Extact High temperatures
TempH = WData{2:366,2};
y = TempH;
%Extract Low temperatures
TempL = WData{2:366,4};
%Extract Avg Temperatures
Tempavg = WData{2:366,3};
%Extract the dates
Dates = WData{2:366,1};
x = Dates;

%plot the temperture variations over the year
plot(x,y) 

[Walter Roberson]

what shows up for class(Dates)? I would not be astonished if it were a cell array of character vectors: depending on how the time is represented in Excel, it might not be interpreted as a datetime.

Also which release are you using?

[Nate Mays]

I attaced an image of what shows up and I'm currenty using R2018b from my school. In excell its set as Date.

[Walter Roberson]

and could you confirm that y is numeric?

R2018b is new enough that datetime plots were supported.

You could experiment with

 plot(datenum(x), y)

[Cris LaPierre]

Please share the full error message (all the red text).

Also, what data type is y?

[Nate Mays]

Error using plot

Invalid data argument.

Error in WeatherExtractionScript (line 21)

plot(x,y)

[Walter Roberson]

please show us the output of

class(x)
class(y)

[Nate Mays]

>> class(x)

ans =

'datetime'

>> class(y)

ans =

'cell'

[Nate Mays]

y is numeric as well

[Walter Roberson]

y is not numeric, y is cell!

Please attach an (extract from) 'WeatherData1.xlsx'

[Nate Mays]

Here is the document. I checked the excel document to make sure that the column with the dates are set as dates and the columns with the weather data is set as numbers.

[Cris LaPierre]

The only issue I see is that you are indexing 266 rows but you only have 265. What version of MATLAB are you using?

%%Use readtable for importing data from excel%%
WData = readtable('WeatherData1.xlsx');

Warning: Column headers from the file were modified to make them valid MATLAB identifiers before creating variable names for the table. The original column headers are saved in the VariableDescriptions property.
Set 'VariableNamingRule' to 'preserve' to use the original column headers as table variable names.

%(1)Determine Temperature Variations throughout the year.
%Extact High temperatures
TempH = WData{2:365,2};
y = TempH;
%Extract Low temperatures
TempL = WData{2:365,4};
%Extract Avg Temperatures
Tempavg = WData{2:365,3};
%Extract the dates
Dates = WData{2:365,1};
x = Dates;

%plot the temperture variations over the year
plot(x,y) 

[Nate Mays]

I'm using R2018b, I changed the 366b to 365 but still getting the same error. is that the only thing you changed?

[Nate Mays]

Nothing is plotted but the date is showing up at the top

[Mathieu NOE]

hello

your code works fine with my R2020b

what do you get as table in WData ?

I get :

WData =

  365×20 table

       Date        Temp____F_    Var3    Var4    DewPoin0___F_    Var6    Var7    Humidity____    Var9    Var10    SeaLevelPress___in_    Var12    Var13    Visibility__mi_    Var15    Var16    Wind__mph_    Var18    Var19    Precip_
    ___________    __________    ____    ____    _____________    ____    ____    ____________    ____    _____    ___________________    _____    _____    _______________    _____    _____    __________    _____    _____    _______

    01-Jan-2011        45         37      29          26           15       9          61          43      24             30.35           30.22    29.98          10            10       10          21         10        25         0  
    02-Jan-2011        49         37      25          20           16      11          74          49      24             30.43           30.33    30.25          10            10       10          10          4        14         0  
    03-Jan-2011        60         45      30          33           26      19          69          50      30             30.23           30.13    30.01          10            10       10          22         10        26         0  
    04-Jan-2011        57         49      40          45           40      33          83          71      59             30.14           30.06    29.98          10            10       10          13          5        15         0  

[Nate Mays]

My WData table looks the same as yours, so you also got a plot as well from the code.

[Mathieu NOE]

and WData dimensions are also 365 x 20 on your side ?

[Nate Mays]

My WData is 366x20

[Nate Mays]

I figured out the issue, My WData had quotations around my number data and after I removed that, I recieved my grpahs and it was plotted correctly

[Nate Mays]

Thank you all for all the help

[Walter Roberson]

The file you posted did not have quotes around the numeric data though ??

[Nate Mays]

It didnt. It wasnt until it was read in that my number databhad quotations.

[Walter Roberson]

You would get that if you tried to read a header. You might need to use detectImportOptions first which was not yet automatic in your release.

[Nate Mays]

Appreciate it will do.

Answer 1

[ANKUR KUMAR]

You can generate dates as per the values in the excel sheet. This won't throw an error for dimension mismatch.

[~, ~, weather_data] = xlsread('WeatherData1.xlsx','Sheet1','A1:B367');
weather_data(cellfun(@(x) ~isempty(x) && isnumeric(x) && isnan(x),weather_data)) = {''};

weather_data=weather_data(3:end,:); 
time=cellfun(@(x) datetime(datestr(datenum(x,'dd-mmm-yy'))) ,weather_data(:,1),'uni',0);
temp=weather_data(:,2);
plot(cat(1,time{:}),cell2mat(weather_data(:,2)))

Hope this helps.

[Nate Mays]

I appreciate it. Thank you.