---
layout: default
title: Query Filtering
---
# Query Filtering
## Query Filters
You can restrict [extract methods](/7.0/reading/) and [conversion methods](/7.0/converting/) output by setting query options. To set those options you will need to use the methods described below. But keep in mind that:
- The query options methods are all chainable *except when they have to return a boolean*;
- The query options methods can be call in any sort of order before any extract/conversion method;
- After an extract/conversion method call, all query options are cleared;
- The optional extract method callable function is called after all query options have been applied;
The options methods are described in the same order as they are applied on the CSV iterator. The order is similar to one found in SQL statement construct.
Starting with version 7.0 The query options can be use to modify the output from the jsonSerialize, toXML and toHTML methods.
Starting with version 7.1 The query options are also available for conversion methods on the League\Csv\Writer class.
## Modifying content methods
### stripBOM($status)
Introduced in version 7.1
`stripBom` only argument `$status` must be a `boolean`. This method specifies if the [BOM sequence](/7.0/bom/) must be removed or not from the CSV's first cell of the first row. The actual stripping will take place only if a BOM sequence is detected and the first row is selected in the resultset **or** if its offset is used as the first argument of the `Reader::fetchAssoc` method.
For backward compatibility, if the method is not called no BOM sequence will be stripped from the CSV document.
The BOM sequence is never removed from the CSV document, it is only stripped from the resultset.
## Filtering methods
The filtering options **are the first settings applied to the CSV before anything else**. The filters follow the *First In First Out* rule.
### addFilter(callable $callable)
The `addFilter` method adds a callable filter function each time it is called. The function can take up to three parameters:
- the current csv row data;
- the current csv key;
- the current csv iterator object;
### removeFilter(callable $callable)
`removeFilter` method removes an already registered filter function. If the function was registered multiple times, you will have to call `removeFilter` as often as the filter was registered. **The first registered copy will be the first to be removed.**
### hasFilter(callable $callable)
`hasFilter` method checks if the filter function is already registered
### clearFilter()
`clearFilter` method removes all registered filter functions.
## Sorting methods
The sorting options are applied **after the CSV filtering options**. The sorting follow the *First In First Out* rule.
To sort the data iterator_to_array is used which could lead to performance penalty if you have a heavy CSV file to sort
### addSortBy(callable $callable)
`addSortBy` method adds a sorting function each time it is called. The function takes exactly two parameters which will be filled by pairs of rows.
### removeSortBy(callable $callable)
`removeSortBy` method removes an already registered sorting function. If the function was registered multiple times, you will have to call `removeSortBy` as often as the function was registered. **The first registered copy will be the first to be removed.**
### hasSortBy(callable $callable)
`hasSortBy` method checks if the sorting function is already registered
### clearSortBy()
`clearSortBy` method removes all registered sorting functions.
## Interval methods
The methods enable returning a specific interval of CSV rows. When called more than once, only the last filtering settings is taken into account. The interval is calculated **after filtering and/or sorting but before extracting the data**.
### setOffset($offset = 0)
`setOffset` method specifies an optional offset for the return data. By default the offset equals `0`.
### setLimit($limit = -1)
`setLimit` method specifies an optional maximum rows count for the return data. By default the offset equals `-1`, which translate to all rows.
Both methods have no effect on the fetchOne method output.
## Examples
### Modifying extract methods output
Here's an example on how to use the query features of the `Reader` class to restrict the `fetchAssoc` result:
```php
function filterByEmail($row)
{
return filter_var($row[2], FILTER_VALIDATE_EMAIL);
}
function sortByLastName($rowA, $rowB)
{
return strcmp($rowB[1], $rowA[1]);
}
$data = $reader
->stripBom(false)
->setOffset(3)
->setLimit(2)
->addFilter('filterByEmail')
->addSortBy('sortByLastName')
->fetchAssoc(['firstname', 'lastname', 'email'], function ($value) {
return array_map('strtoupper', $value);
});
// data length will be equals or lesser that 2 starting from the row index 3.
// will return something like this :
//
// [
// ['firstname' => 'JANE', 'lastname' => 'RAMANOV', 'email' => 'JANE.RAMANOV@EXAMPLE.COM'],
// ['firstname' => 'JOHN', 'lastname' => 'DOE', 'email' => 'JOHN.DOE@EXAMPLE.COM'],
// ]
//
```
### Modifying conversion methods output
Starting with `version 7.0`, the query options can also modify the output from the conversion methods as shown below with the `toHTML` method.
```php
function filterByEmail($row)
{
return filter_var($row[2], FILTER_VALIDATE_EMAIL);
}
function sortByLastName($rowA, $rowB)
{
return strcmp($rowB[1], $rowA[1]);
}
$data = $reader
->stripBom(true)
->setOffset(3)
->setLimit(2)
->addFilter('filterByEmail')
->addSortBy('sortByLastName')
->toHTML("simple-table");
// $data contains the HTML table code equivalent to:
//
//
// | JANE | RAMANOV | JANE.RAMANOV@EXAMPLE.COM |
// | JOHN | DOE | JOHN.DOE@EXAMPLE.COM |
//
//
```