How to extract the data from webread output?

Could someone please help me with understanding how to extract the data from webread output?

The question is as follows:

I am loading the data from the server, and need to be able to ready it in Matlab as a table or mat file. The problem is that it is either a string from json code or a struct with many layers, and I do not quite understand how to extract variables that are linked together.

The code is a follows:

----

key = 'Q.N.DE.W2.S11.S13.N.A.LE.F4.T._Z.XDC._T.S.V.N._T'

api = 'https://sdw-wsrest.ecb.europa.eu/service/'

url = [api 'data/QSA/' key];

options2 = weboptions('ContentType','text');

data2 = webread(url)%,options)

data1= webread(url,options2)

---

And I would like to be able to extract: these two linked variables:

<generic:ObsDimension value="2021-Q1"/>

<generic:ObsValue value="7854"/>

The first one-- as a string and the second one -- as a number.

Answer 1

[Ive J]

It's always better to first check the RESTful API documentations. In your case, you can get those values either by applying regexp to XML contents, or read/decode it in JSON format:

key = 'Q.N.DE.W2.S11.S13.N.A.LE.F4.T._Z.XDC._T.S.V.N._T';
api = 'https://sdw-wsrest.ecb.europa.eu/service/';
url = [api 'data/QSA/' key];
raw = webread(url);

data = jsondecode(raw);

% get ids/values
ObsDimension = {data.structure.dimensions.observation.values.id}.';
ObsValue = struct2table(data.dataSets.series.x0_0_0_0_0_0_0_0_0_0_0_0_0_0_0_0_0_0.observations); % ObsValue are stored here

% create a new table from these 2 arrays
res = table(ObsDimension, ObsValue{1, :}.', 'VariableNames', {'ObsDimension', 'ObsValue'})

res = 89×2 table
    ObsDimension    ObsValue
    ____________    ________

    {'1999-Q1'}          0  
    {'1999-Q2'}          0  
    {'1999-Q3'}          0  
    {'1999-Q4'}          0  
    {'2000-Q1'}        991  
    {'2000-Q2'}       1042  
    {'2000-Q3'}       1093  
    {'2000-Q4'}       1143  
    {'2001-Q1'}       1237  
    {'2001-Q2'}       1330  
    {'2001-Q3'}       1424  
    {'2001-Q4'}       1518  
    {'2002-Q1'}       1679  
    {'2002-Q2'}       1840  
    {'2002-Q3'}       2001  
    {'2002-Q4'}       2162  

You could also use regexp:

key = 'Q.N.DE.W2.S11.S13.N.A.LE.F4.T._Z.XDC._T.S.V.N._T';
api = 'https://sdw-wsrest.ecb.europa.eu/service/';
url = [api 'data/QSA/' key];
opts = weboptions('ContentType', 'text');
raw = webread(url, opts);
ObsDimensionNew = regexp(raw, '(?<=<generic:ObsDimension value=")(.*?)[^"/>]*', 'match').';
ObsValueNew = regexp(raw, '(?<=<generic:ObsValue value=")(.*?)[^"/>]*', 'match').';
resNew = table(ObsDimensionNew, ObsValueNew, 'VariableNames', {'ObsDimension', 'ObsValue'})

resNew = 89×2 table
    ObsDimension    ObsValue
    ____________    ________

    {'1999-Q1'}     {'0'   }
    {'1999-Q2'}     {'0'   }
    {'1999-Q3'}     {'0'   }
    {'1999-Q4'}     {'0'   }
    {'2000-Q1'}     {'991' }
    {'2000-Q2'}     {'1042'}
    {'2000-Q3'}     {'1093'}
    {'2000-Q4'}     {'1143'}
    {'2001-Q1'}     {'1237'}
    {'2001-Q2'}     {'1330'}
    {'2001-Q3'}     {'1424'}
    {'2001-Q4'}     {'1518'}
    {'2002-Q1'}     {'1679'}
    {'2002-Q2'}     {'1840'}
    {'2002-Q3'}     {'2001'}
    {'2002-Q4'}     {'2162'}

[Veronika Stolbova]

Thank you so much!

It is exactly what I needed. Works like a charm!

[Peter Perkins]

Even better, create a timetable, something like

>> ObsDimension = datetime(ObsDimension,'Format','uuuu-QQQ');
>> res = timetable(ObsValue{1, :}.', 'RowTimes',ObsDimension, 'VariableNames',{'ObsValue'});
>> head(res)
ans =
  8×1 timetable
     Time      ObsValue
    _______    ________
    1999-Q1         0  
    1999-Q2         0  
    1999-Q3         0  
    1999-Q4         0  
    2000-Q1       991  
    2000-Q2      1042  
    2000-Q3      1093  
    2000-Q4      1143  

[Veronika Stolbova]

Thanks a lot!