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# rarity\_sum

`rarity_sum(str fieldname)`calculates the rarity score for matched keywords. The function calculates the score over keywords or lists of keywords, using the TF-IDF formula. 

### Input

* <mark style="color:purple;">fieldname1</mark> (str) - the name of the field to match in query document. params\[fieldname1] must be of type **keyword** or **list\[keyword]**
* <mark style="color:purple;">fieldname2</mark> (str, default=fieldname1) - the name of the field to match in database document. V\[fieldname2] must be of type **keyword** or **list\[keyword]**

### Output

* <mark style="color:purple;">(float)</mark> - TF-IDF for the matched keywords. If params\[fieldname] and params\[fieldname] are lists of, the function will return the **sum of rarity score out of** all matched keywords

**Example:**

```python
Score = rarity_sum("cities")
```

The function will return the sum of rarity scores of all matched keywords between params\["cities"] and V\["cities"]


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