# CoalesceFilter **`class CoalesceFilter(config)`** Bases: [`Filter`](squirro.lib.nlp.steps.filters.Filter.md#squirro.lib.nlp.steps.filters.Filter) The coalesce [`Filter`](squirro.lib.nlp.steps.filters.Filter.md#squirro.lib.nlp.steps.filters.Filter) returns the first value which is set from a list of fields. Any string or list is accepted as the valid value, None is treated as not having been set. **Input** - any type can be used for the input fields. **Output** - the output field is filled with data of type [`str`](https://docs.python.org/3.11/library/stdtypes.html#str). Parameters - `type` ([`str`](https://docs.python.org/3.11/library/stdtypes.html#str)) – coalesce - `input_fields` ([`list`](https://docs.python.org/3.11/library/stdtypes.html#list)) – Fields to look at - `output_field` ([`str`](https://docs.python.org/3.11/library/stdtypes.html#str)) – Field to store the resulting value **Example** ```json { "step": "filter", "type": "coalesce", "input_fields": ["clean_body", "body"], "output_field": "processing_body" } ``` Methods SummaryMethods Documentation **`process_doc(doc)`** Process a document Parameters `doc` ([`Document`](../technical/libnlp/base.md#squirro.lib.nlp.document.Document)) – Document Returns Processed document Return type [Document](../technical/libnlp/base.md#squirro.lib.nlp.document.Document)