How to add search by category in magento mini search

There is no free extension in magento commerce which will help you to search your store with particular category. I tried from myself and able to do, I am sharing my exprerience here with.

First create the drop down list of all category in form.mini.phtml

<select name="category" id="category_search_field">
<option value="">-- Any Category --</option>
<?php foreach ($catalog->getStoreCategories() as $_category): ?>
<?php if($_category->hasChildren()): ?>
<option class="parent-cat" value="<?php echo $_category->getId(); ?>"><?php echo $_category->getName();?></option>
<?php foreach ($_category->getChildren() as $subcategory):
if($subcategory->getIsActive()) : ?>
<option value="<?php echo $subcategory->getId(); ?>"<?php echo ($this->getRequest()->getQuery('category') == $subcategory->getId() ? ' selected="selected"': "") ?>><?php echo $subcategory->getName(); ?></option>
<?php endif; endforeach; ?>
<?php elseif($_category->getIsActive()): ?>
<option value="<?php echo $_category->getId(); ?>"><?php echo $_category->getName();?></option>
<?php endif; ?>
<?php endforeach ?>
</select>

Now go to app/code/core/Mage/CatalogSearch/Helper and open the Data.php and add the below code

public function getStoreCategories()
{
$helper = Mage::helper('catalog/category');
return $helper->getStoreCategories();
}
public function getSelectedCategory()
{
$catid = (int)addslashes($_REQUEST['category']);
$cat="";
if($catid>1)
$cat = Mage::getModel('catalog/category')->load($catid);
return $cat;
}

Now go to app/code/core/Mage/CatalogSearch/Model and open the Layer.php

replace

public function prepareProductCollection($collection)
{
$collection
->addAttributeToSelect(Mage::getSingleton('catalog/config')->getProductAttributes())
->addSearchFilter(Mage::helper('catalogsearch')->getQuery()->getQueryText())
->setStore(Mage::app()->getStore())
->addMinimalPrice()
->addFinalPrice()
->addTaxPercents()
->addStoreFilter()
->addUrlRewrite();
Mage::getSingleton('catalog/product_status')->addVisibleFilterToCollection($collection);
Mage::getSingleton('catalog/product_visibility')->addVisibleInSearchFilterToCollection($collection);
return $this;
}

with

public function prepareProductCollection($collection)
{
if(Mage::helper('catalogsearch')->getSelectedCategory()!="")
{
$collection
->addAttributeToSelect(Mage::getSingleton('catalog/config')->getProductAttributes())
->addSearchFilter(Mage::helper('catalogsearch')->getQuery()->getQueryText())
->setStore(Mage::app()->getStore())
->addMinimalPrice()
->addFinalPrice()
->addTaxPercents()
->addStoreFilter()
->addCategoryFilter(Mage::helper('catalogsearch')->getSelectedCategory())
->addUrlRewrite();
}
else
{
$collection
->addAttributeToSelect(Mage::getSingleton('catalog/config')->getProductAttributes())
->addSearchFilter(Mage::helper('catalogsearch')->getQuery()->getQueryText())
->setStore(Mage::app()->getStore())
->addMinimalPrice()
->addFinalPrice()
->addTaxPercents()
->addStoreFilter()
->addUrlRewrite();
}
Mage::getSingleton('catalog/product_status')->addVisibleFilterToCollection($collection);
Mage::getSingleton('catalog/product_visibility')->addVisibleInSearchFilterToCollection($collection);

return $this;
}

save and Enjoy.