Many of you may know Ned from various parts of MATLAB Central, such as the community blog "MATLAB Spoken Here". If you're a frequent visitor of MATLAB Central, you may have also visited Trendy, which allows you to quickly query and plot trends from the web. One of the utility functions provided within Trendy has been urlfilter, and it's a convenient function that allows you to easily scrape data from a web page. Now, you can use urlfilter outside of Trendy!
Let's say that I want to grab and plot the high and low temperatures in Natick, MA for the next 10 days. I will grab data from this URL at http://www.wunderground.com. As you can see from the web page, the 10-day forecast is displayed about halfway down the page in a table. Each day has a header in the format of "day of week, day", e.g. "Friday, 17".
First, I calculate the days I'm interested in, which is today to 10 days from today. I also determine the day of the week using the weekday function. I need this information, because urlfilter will use this to scrape the necessary data.
days = floor(now):floor(now)+9; [~, ~, dayval] = datevec(days); [~, weekdaystr] = weekday(days, 'long');
Now, I simply use urlfilter to iterate through each day as the search term.
% Pre-allocate variables low = nan(1,length(days)); high = nan(1,length(days)); url = 'http://www.wunderground.com/q/zmw:01760.1.99999'; for iD = 1:length(days) % Search term str = [strtrim(weekdaystr(iD,:)), ', ', num2str(dayval(iD))]; disp(['Scraping temperatures for "', str, '"...']) % Fetch 2 values (high and low) vals = urlfilter(url,str,2); high(iD) = vals(1); low(iD) = vals(2); end
Scraping temperatures for "Friday, 17"... Scraping temperatures for "Saturday, 18"... Scraping temperatures for "Sunday, 19"... Scraping temperatures for "Monday, 20"... Scraping temperatures for "Tuesday, 21"... Scraping temperatures for "Wednesday, 22"... Scraping temperatures for "Thursday, 23"... Scraping temperatures for "Friday, 24"... Scraping temperatures for "Saturday, 25"... Scraping temperatures for "Sunday, 26"...
Let's plot the results. To show the temperature in two different units, I'm using my plot2axes (shameless plug).
ax = plot2axes(days,high,'r.-',days,low,'b.-', ... 'YScale',@(x)5/9*(x-32)); ylabel(ax(1),'Temperature (\circF)') ylabel(ax(2),'Temperature (\circC)') datetick('x','mmm dd','keepticks') legend('High','Low') title('10-day Forecast for Natick, MA, U.S.A')
Note that I could have done this more efficiently with a single call to urlfilter, extracting about 40 numbers at once, and then parsing the numbers to get the necessary high and low temperatures. I used the above approach to make it easier to understand.
Get the MATLAB code
Published with MATLAB® R2013b
3 CommentsOldest to Newest
Very cool pick! If you append another input called ‘occurrence’ to Ned’s urlfilter.m and the following line of code below line 38 in urlfilter.m
strIndex = strIndex(occurrence);
then you can run the following script (adapted from your excellent example) to get a more universal weather report ;) The script scrapes NOAA’s forecast of the 10cm flux of the Sun.
% solarFlux.m % Scrape NOAA's forecast of the 10cm flux of the Sun. days = floor(now):floor(now)+44; dayval = datestr(days,'ddmmmyy'); % Pre-allocate variables flux = nan(1,length(days)); url = 'http://www.swpc.noaa.gov/ftpdir/latest/45DF.txt'; for iD = 1:length(days) % Search term str = dayval(iD,:); disp(['Scraping F10.7cm Flux for "', str, '"...']) flux(iD) = urlfilter(url,str,1,'forward',2); end plot(days,flux,'r.-'); ylabel('F10.7cm Flux (10^-22 W m^-2 Hz^-1)') datetick('x','dd mmm','keepticks') title('45-day F10.7cm Flux for the Sun')
I would like to scrape this page of wunderground http://www.wunderground.com/cgi-bin/findweather/getForecast?hourly=1&query=zmw:00000.1.16105&yday=28&weekday=Mercoled%C3%AC&MR=1 and I would like that matlab automatically scrapes wehater data every day for the next 3 days. Is it possible to do it reaaaranging this code?
Thanks a lot
Yes, you should be able to use “urlfilter” to scrape data from the page. The key is to find the keyword in the web page near the value that you are interested in and capture the result for any postprocessing.
Also, check out Trendy. It’s set up to automatically scrape the data every day.
Thanks for this! I like the “occurrence” option. That provides additional flexibility to make it easier to scrape data. Can you suggest the enhancement to Ned?