# Skimming

Ntuple skimming is very easy to do in NAIA. You can setup a new file for your skimmed ntuples by calling
`NAIAChain::CreateSkimTree` and specifying the name of the output root file 
([see doxygen](https://naia-docs.web.cern.ch/naia-docs/v1.1.0/classNAIA_1_1NAIAChain.html#aeca79ddd1a0f42ede2f82642087d91ed)). 

`CreateSkimTree` will return a `SkimTreeHandle` [object](https://naia-docs.web.cern.ch/naia-docs/v1.1.0/classNAIA_1_1SkimTreeHandle.html). 
As the name implies the `SkimTreeHandle` is a handle to the new tree, you can call `Fill` on it to save a given event
in the new tree.

When you're done processing you can call `Write` on the `SkimTreeHandle` to write the resulting `TTree` on the
output root file.

```{note}
If you don't want to write out some containers (in case you know you won't need them and want to save some space)
you can pass a semicolon-separated list of containers to exclude as the second argument of ``CreateSkimHandle``. 
```