Concatenation revisited

Now that Paul Donnelly has shown us the way, let’s look at another way to concatenate elements from items that uses YQL and the Web Service module.

This pipe starts off in the same way as the pipe in my previous post on concatenation, with a URL Input, an Item Builder and a Fetch Feed in a Loop.

Here we use Rename to make a copy of the items (in item.stuff) to an element yql_array. That’s a specific name that will be used by the YQL web service. On the right is a URL Builder with the elements:

• Base – http://query.yahooapis.com
• Path – v1/public/yql
• Parameters
  • q – use http://pdaniel.co.uk/yql/array_concat.xml as array_concat; select * from array_concat where data = @data and delim=@delim and ele=@ele
    This is the YQL statement at the heart of this method. The use clause links to a YQL open data table with an  Execute clause in it, and gives that table a name of array_concat. The select clause is going to pass values for “data”, “delim” and “ele” to the open table. The values for these are specified using YQL variable substitution. It looks like the @data substitution is special, since we ourselves don’t supply a value for it.
  • format – json. That’s the format the Web Service uses.
  • diagnostics – If you’re having problems with a YQL statement you can set this to “true” and get diagnostic information.
  • delim – One of the @ variables that were used. The delim value is a separator for each of the elements we’re going to collect.
  • ele – the element name. In this case we’re concatenating title elements.

In the Web Service module the path is set to query.results.result.items.

The result of the concatenation is always returned in the yql_array_string element. The rest of the pipe then works on that string to produce the desired output.

This approach isn’t just limited to working on whole items as we can use it to concatenate array elements within an item. In this pipe, for instance, category values within an item are being concatenated. This is how the data looks to start with:

In the Rename module we have

and in the URL Builder we have

Update: 10th June. The ele parameter is now optional. This allows for arrays such as category.0, category.1 as well as category.0.title, category.1.title.

Tags: Yahoo Pipes