how to find a specific value from a textfile(3000 lines), when the value keeps on changing its location in the file

In my code, I have to download weather data every hour from the website ( http://api.met.no/weatherapi/locationforecast/1.9/?lat=52.37;lon=4.89;msl=1) I am able to do so but now i need to find the value for "cloudiness" for the time period 24 hours after it was downloaded. I just need numerical value of cloudiness. I tried getting that data by importing data from that specific cell, but the value keeps on changing its value location. So I need to update the cell location for every time I run my code.How should I get the exact numerical value.

For example: I want the cloudiness for the date "from="2015-03-12T11:00:00Z" to="2015-03-12T11:00:00Z"

The code goes like this:

 <time datatype="forecast" from="2015-03-12T11:00:00Z" to="2015-03-12T11:00:00Z">
         <location altitude="1" latitude="53.0500" longitude="4.8000">
            <temperature id="TTT" unit="celsius" value="8.3"/>
            <windDirection id="dd" deg="138.0" name="SE"/>
            <windSpeed id="ff" mps="4.5" beaufort="3" name="Lett bris"/>
            <humidity value="62.9" unit="percent"/>
            <pressure id="pr" unit="hPa" value="1030.9"/>
            *<cloudiness id="NN" percent="0.0"/>*
            <fog id="FOG" percent="0.0"/>
            <lowClouds id="LOW" percent="0.0"/>
            <mediumClouds id="MEDIUM" percent="0.0"/>
            <highClouds id="HIGH" percent="0.0"/>
            <dewpointTemperature id="TD" unit="celsius" value="1.6"/>
         </location>
      </time>
      <time datatype="forecast" from="2015-03-12T10:00:00Z" to="2015-03-12T11:00:00Z">
         <location altitude="1" latitude="53.0500" longitude="4.8000">
            <precipitation unit="mm" value="0.0" minvalue="0.0" maxvalue="0.0"/>
<symbol id="Sun" number="1"/>
         </location>
      </time>
      <time datatype="forecast" from="2015-03-12T09:00:00Z" to="2015-03-12T11:00:00Z">
         <location altitude="1" latitude="53.0500" longitude="4.8000">
            <precipitation unit="mm" value="0.0" minvalue="0.0" maxvalue="0.0"/>
<symbol id="Sun" number="1"/>
         </location>
      </time>
      <time datatype="forecast" from="2015-03-12T08:00:00Z" to="2015-03-12T11:00:00Z">
         <location altitude="1" latitude="53.0500" longitude="4.8000">
            <precipitation unit="mm" value="0.0" minvalue="0.0" maxvalue="0.0"/>
<symbol id="Sun" number="1"/>
         </location>
      </time>
      <time datatype="forecast" from="2015-03-12T05:00:00Z" to="2015-03-12T11:00:00Z">
         <location altitude="1" latitude="53.0500" longitude="4.8000">
            <precipitation unit="mm" value="0.0" minvalue="0.0" maxvalue="0.0"/>
<symbol id="LightCloud" number="2"/>
         </location>
      </time>

This is one basic data in the file. Now i want to get numerical data (for cloudiness) in the line 10.

What will be the best way to read the particular data?

Answer 1

[Guillaume]

Since your document is an xml file, the most reliable way would be to use xml parsing and navigate the dom to find the information of interest:

xdom = xmlread('http://api.met.no/weatherapi/locationforecast/1.9/?lat=52.37;lon=4.89;msl=1');
cloudtags = xdom.getElementsByTagName('cloudiness');
cloudiness = cell(cloudtags.getLength, 3); 
for item = 1 : cloudtags.getLength
   cloudtag = cloudtags.item(item - 1);
   cloudiness{item, 1} = str2double(cloudtag.getAttribute('percent'));
   timetag = cloudtag.getParentNode.getParentNode;
   cloudiness{item, 2} = char(timetag.getAttribute('from'));
   cloudiness{item, 3} = char(timetag.getAttribute('to'));
end
cloudiness

[Punit Gandhi]

Thank you for your answer. It perfectly works. Though, further I want to know, how can I get cloudiness for a particular date and time (like for time: '2015-03-12T05:00:00Z' '2015-03-12T05:00:00Z')?

[Guillaume]

matchrow = strcmp(cloudiness(:, 2), '2015-03-12T05:00:00Z') & strcmp(cloudiness(:, 3), '2015-03-12T05:00:00Z');
matchcloudiness = cloudiness{matchrow, 1}

[Punit Gandhi]

Thank you for your help

[Punit Gandhi]

Can you help me optimize the code which you helped me write.

http://nl.mathworks.com/matlabcentral/answers/196243-my-matlab-code-is-giving-me-this-error-too-many-outputs-requested-if-someone-can-help-me-solve-th