caption: subfilter
created: 20181031175129475
modified: 20211217135706478
op-input: a [[selection of titles|Title Selection]] passed as input to the subfilter
op-neg-input: a [[selection of titles|Title Selection]] passed as input to the subfilter
op-neg-output: those input titles that are <<.em not>> returned from the subfilter  <<.place S>>
op-output: the [[selection of titles|Title Selection]] returned from the subfilter <<.place S>>
op-parameter: a [[filter expression|Filter Expression]]
op-parameter-name: S
op-purpose: select titles from the parameter interpreted as a [[filter expression|Filter Expression]]
tags: [[Filter Operators]] [[Field Operators]] [[Selection Constructors]] [[Negatable Operators]] [[Selection Constructors: Conditional]]
title: subfilter Operator
type: text/vnd.tiddlywiki

<<.from-version "5.1.18">> Note that the <<.op subfilter>> operator was introduced in version 5.1.18 and is not available in earlier versions.

<<.tip " Literal filter parameters cannot contain square brackets but you can work around the issue by using a variable:">>

```
<$set name="myFilter" value="[tag[one]]">
<$list filter="[all[tiddlers]subfilter<myFilter>]">
...
```

<<.tip "Compare with the similar [[filter|filter Operator]] operator which runs a subfilter against each title, returning those titles that return a non-empty list (and discards the results of the subfilter)">>

The <<.op subfilter>> operator will act as a [[constructor|Selection Constructors]] whenever the filter defined by its parameter is a [[constructor|Selection Constructors]]. Otherwise, it will act as a [[modifier|Selection Constructors]].

<<.operator-examples "subfilter">>