How to do a Loop statement from cell to double?

Hi there

I have a file with wind information (direction and speed), the wind direction has this format (E, N, NE,...) I would like to do a wind rose from 1989 to 2019, so I have a file.xls with multiple sheets (from 1989 to 2019). I'm trying to convert the wind direction from (E, N, NE to 90, 0 , 45). But I do not know how to do it, any help? I post the file (1989.xlsx) and what I've been doing.

%% I created a artificial data to organized wind speed and direction  
t1 = datetime(1989,01,01,00,00,00);
t2 = datetime(2019,12,31,23,00,00);
t = (t1:hours(1):t2)';

% my idea is to convert ('E', 'N'... to 90, 0) to the 30 years.
for i = length(1989.VarName1(10:40))
    if 1989.Dir{10:40},'E' == 1;
        1989.Dir(10:40)= 90;
    end
end

Answer 1

[dpb]

Use ordinal categorical variables --

t1989=readtable('1989.xlsx','Range','10:40','ReadVariableNames',0);     % get in a set of data to play with
tTmp=t1989(1:10,1:3);        % just keep 10 rows of the first direction column for illustration
tTmp.Properties.VariableNames={'Dia','Dir','Vel'};      % assign meaningful variable names

This gives us the following table for starters; you'll obviously work over the whole table and all months. There's a problem with the spreadsheet organization for reading default variable names since are duplicated for each of the twelve months; but that is just some bookkeeping to fix up however you choose to to so.

tTmp =
  10×3 table
    Dia    Dir     Vel  
    ___    ___    ______
     1     E      5.2083
     2     SE     7.1667
     3     ESE    6.3333
     4     ENE    5.9167
     5     NE       8.25
     6     NNE      9.75
     7     NW     10.667
     8     N      11.292
     9     NW     9.1667
    10     N      4.9583
>>

OK, now to the meat of the problem...first convert the direction to a categorical ordinal variable in the defined sequence clockwise from N

t1989.Var2=categorical(t1989.Var2,{'N';'NNE';'NE';'ENE'; ...
                                    'E';'ESE';'SE';'SSE'; ...
                                    'S';'SSW';'SW';'WSW'; ...
                                    'W';'WNW';'NW';'NNW'}, 'Ordinal',1);
tTmp.Theta=(double(tTmp.Dir)-1)*22.5;   % calculate/store wind angular direction from direction

The above leaves us with--

tTmp =
  10×4 table
    Dia    Dir     Vel      Theta
    ___    ___    ______    _____
     1     E      5.2083       90
     2     SE     7.1667      135
     3     ESE    6.3333    112.5
     4     ENE    5.9167     67.5
     5     NE       8.25       45
     6     NNE      9.75     22.5
     7     NW     10.667      315
     8     N      11.292        0
     9     NW     9.1667      315
    10     N      4.9583        0
>> 

where the Theta variable is the wind direction in compass degrees associated with the named direction.

Note that is is mandatory to use the 'ordinal' type to indicate the named list of categories is ordered in the direction given on the conversion.

Answer 2

[Fabian Moreno]

Thank you a lot, it works perfectly.