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<!DOCTYPE html>
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<title>Diggernaut: Documentation for Meta-Language | Iterators | Introduction</title>
<meta name="description" content="We learn to iterate over the main logic block of the scraper with different arguments.">
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<h1>Iterators</h1>
<div>
<h2>Introduction</h2>
<p class="flow-text">
Iterators are used to generate a list of argument sets that are used
for iteration over the main block of the digger logic. Other words, the digger performs the basic
logic for each element of the list, where each element is a set of arguments.
</p>
<p class="flow-text">
Typically, an iterator is used when you need to do search on the website using different sets of parameters
as search arguments, or when you need to collect data for certain dates, using the date as the query argument.
</p>
<p class="flow-text">
Currently, iterators of three types are supported:<br/>
<span class="hlt2">date</span> - dates based iterators<br/>
<span class="hlt2">csv</span> - keeps single field and multiple values for this field in CSV format<br/>
<span class="hlt2">fieldset</span> - keeps fieldsets with values.
</p>
<p class="flow-text">
You can use multiple iterators of same or different types, in this case the system will combine all the iterators
and create a single iterator with all possible sets of fields and values. This allows you to create shorter records for
repeated values. For example, if we want to create an iterator that has several fields, the best option would be to use
the <span class = "hlt2">fieldset</span>. But if one of the fields takes values from 1 to 10, then we will have to put
this fieldset 10 times in configuration. So using combination of <span class = "hlt2">csv</span> and <span class = "hlt2">fieldset</span>
iterators can shorten the iterator entry:
</p>
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<div class="col s12">
<pre class="language-yaml">
<code class="language-yaml">iterator:
# DESCIBING BASIC FIELDSET
- type: fieldset
fields:
- season: fall
category: athletics
# DESCRIBING FIELD WHICH HAS MULTIPLE VALUES
- type: csv
name: age
value: 1,2,3,4,5,6,7,8,9,10
</code></pre>
</div>
</div>
<p class="flow-text">
As a result, the following list of sets of arguments will be formed, and digger
will execute main logic block for each set from this list:
</p>
<div class="row">
<div class="col s12">
<pre class="language-json">
<code class="language-json">[
{ "season": "fall", "category": "athletics", "age": 1 },
{ "season": "fall", "category": "athletics", "age": 2 },
{ "season": "fall", "category": "athletics", "age": 3 },
{ "season": "fall", "category": "athletics", "age": 4 },
{ "season": "fall", "category": "athletics", "age": 5 },
{ "season": "fall", "category": "athletics", "age": 6 },
{ "season": "fall", "category": "athletics", "age": 7 },
{ "season": "fall", "category": "athletics", "age": 8 },
{ "season": "fall", "category": "athletics", "age": 9 },
{ "season": "fall", "category": "athletics", "age": 10 }
]
</code></pre>
</div>
</div>
<p class="flow-text">
As you can see, using a combination of iterators, you can quickly and conveniently describe different sets of arguments.
Next, we'll see in details into each type of iterator and we will start with <span class = "hlt2">date</span> iterators.
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