Array indices must be positive integers or logical values "ERROR"

I keep getting this error(below) but im not sure why, anyone have any idea what is happening? Thanks

Array indices must be positive integers or logical values.

Error in DepthofWater (line 20)

my_url = strcat('https://', base_url, province, '/', frequency, '/', province, '_', station_id(i), '_', frequency, '_hydrometric.', file_type)

base_url = 'dd.weather.gc.ca/hydrometric/csv/'
province = 'ON';
frequency = 'daily';
file_type = 'csv';
station_id =['02HA014','02HC030','02HC028','02HC027']
station_name =["REDHILL CREEK AT HAMILTON",...
    "ETOBICOKE CREEK BELOW QUEEN ELIZABETH HIGHWAY",...
    "LITTLE ROUGE CREEK NEAR LOCUST HILL",...
    "BLACK CREEK NEAR WESTON"]

for s=1:1:length(station_id)
    
  my_url = strcat('https://', base_url, province, '/', frequency, '/', province, '_', station_id(i), '_', frequency, '_hydrometric.', file_type)

  gauge_data = webread(my_url);
  depth_data = gauge_data.WaterLevel_NiveauD_eau_m_.';
  depth_data(find(isnan(depth_data)))=[];

%   figure (s)
%   %plot(depth_data)
%   xlabel('historical daily water level(day)');
%   ylabel('water level (m)');
%   title(['daily water level at ', station_name(s), 'ID:' , station_id(s)]);

% define some arbitrary data
y = depth_data;
x = 1:1:length(y);
% calculate avg & standarddeviation
avg_y_scalar = mean(y);
avg_y_vector = avg_y_scalar * ...
     ones(1,length(y));
std_y = std(y);

% data + 1 std deviation (above)
y_plus = y + std_y;     
% data -1 std deviation (below)
y_minus = y -std_y;    

% create a vector of the avg-std_dev that are in reverse order
j=1;
for i = length(y):-1:1
  y_minus_reverse(j) = y_minus(i);
  j=j+1;     % increment j positive
end

% create plot
figure(s)

% plot the data andaverage
plot(x,y,'b',x,avg_y_vector);             

% plot std deviation shape
patch([1:1:length(y) ...
length(y):-1:1],...
[y_plus y_minus_reverse],...
'b',...
'facealpha',0.05,...% fill colour 
'edgecolor','r',...
'edgealpha',0.05) % edge colour

% Legend, Title, axis labels.
%figure (s)
  %plot(depth_data)
  xlabel('historical daily water level(day)');
  ylabel('water level (m)');
  title(['daily water level at ', station_name(s), 'ID:' , station_id(s)]);
legend('original data',...
'average values',...
'standard deviation')

  s=s+1
end

Answer 1

[Walter Roberson]

for s=1:1:length(station_id)
    
  my_url = strcat('https://', base_url, province, '/', frequency, '/', province, '_', station_id(i), '_', frequency, '_hydrometric.', file_type)

Your variable i has not been defined at that line, so it will have the default value in MATLAB of sqrt(-1) .

Note by the way that your s variable from for s is not being used in the loop.

[Sakibur Rahman]

oh wait so i should change the s to i then right?

[Walter Roberson]

Probably. Or change i to s.

[Sakibur Rahman]

ok i changed i to s and now i get this error

Error using patch

Vectors must be the same length.

Error in Waterdepth (line 62)

patch([1:1:length(y) ...

[Sakibur Rahman]

ok so now i figured out how to get the graphs, i am getting the graphs with the proper data, however my std deviation shape calculation isnt working, after it goes through the first graph it stops and says as above, so i know now that i am getting the proper data now the problem is with this patch function, any ideas?

[Walter Roberson]

You have

j=1;
for i = length(y):-1:1
  y_minus_reverse(j) = y_minus(i);
  j=j+1;     % increment j positive
end

Is there a reason you are not just using fliplr(y_minus) ?

[Sakibur Rahman]

what is fliplr ? Never learned or been shown that in class.

edit: oh so that just flips the array in left/right direction, so basically what im doing here but much less complicated?

[Walter Roberson]

Yup, less complicated and more clear.

You can also do

y_minus_reverse = y_minus(end:-1:1);

which accomplishes the reversal through plain indexing.

[Sakibur Rahman]

oh ok thanks, but for my problem now, it seems my program isnt showing the standard deviation and say error using the patch and that the vectors must be the same length, im a bit confused by that.

[Joe Vinciguerra]

I took the recommendations from Walter and applied them here (plus a couple insignificant changes such as 1:length(station_id) instead of 1:1:length(station_id). It seeems the source of this latest error is resolved by using y_minus_reverse = fliplr(y_minus); as Walter recommended. This seemed to work for me.

base_url = 'dd.weather.gc.ca/hydrometric/csv/';
province = 'ON';
frequency = 'daily';
file_type = 'csv';
station_id =["02HA014";"02HC030";"02HC028";"02HC027"];
station_name =["REDHILL CREEK AT HAMILTON",...
	"ETOBICOKE CREEK BELOW QUEEN ELIZABETH HIGHWAY",...
    "LITTLE ROUGE CREEK NEAR LOCUST HILL",...
    "BLACK CREEK NEAR WESTON"];

for s=1:length(station_id)
	my_url = strcat('https://',...
        base_url,...
        province, '/',...
        frequency, '/',...
        province, '_',station_id(s), '_', frequency, '_hydrometric.', file_type);

	gauge_data = webread(my_url);
	depth_data = gauge_data.WaterLevel_NiveauD_eau_m_.';
	depth_data(find(isnan(depth_data)))=[];

%     figure (s)
%     plot(depth_data)
%     xlabel('historical daily water level(day)');
%     ylabel('water level (m)');
%     title(['daily water level at ', station_name(s), 'ID:' , station_id(s)]);

    % define some arbitrary data
    y = depth_data;
    x = 1:length(y);
    
    % calculate avg & standarddeviation
    avg_y_scalar = mean(y);
    avg_y_vector = avg_y_scalar * ...
         ones(1,length(y));
    std_y = std(y);

    % data + 1 std deviation (above)
    y_plus = y + std_y;     
    % data -1 std deviation (below)
    y_minus = y -std_y;    

    % create a vector of the avg-std_dev that are in reverse order
    y_minus_reverse = fliplr(y_minus);

    % create plot
    figure(s)

    % plot the data andaverage
    plot(x,y,'b',x,avg_y_vector);             

    % plot std deviation shape
    patch([1:length(y) length(y):-1:1],...
        [y_plus y_minus_reverse],...
        'b',...
        'facealpha',0.05,...% fill colour 
        'edgecolor','r',...
        'edgealpha',0.05) % edge colour

    % Legend, Title, axis labels.
% 	figure (s)
% 	plot(depth_data)
    xlabel('historical daily water level(day)');
    ylabel('water level (m)');
    title(['daily water level at ', station_name(s), 'ID:' , station_id(s)]);
    legend('original data',...
        'average values',...
        'standard deviation')

end

[Sakibur Rahman]

Thanks a lot, I was using the fliplr incorrectly and thats why I was still getting an error. Tried your way and it works perfectly. Thanks everyone.