Devoxx - filter, partition and offset (original) (raw)

William Clark wclark1324 at comcast.net
Wed Apr 3 19:37:27 PDT 2013

Add to that Python: http://docs.python.org/2/library/functions.html#filter

and the JDK itself uses filter in the same sense for a few types:

http://docs.oracle.com/javase/6/docs/api/java/util/logging/Filter.html http://docs.oracle.com/javase/6/docs/api/javax/swing/RowFilter.html http://docs.oracle.com/javase/6/docs/api/javax/swing/filechooser/FileFilter.html (and FilenameFilter)

The JDK is explicit in at least one case I can think of: Collection.retainAll and .removeAll. Maybe someone else can think of an example where the JDK uses filter in the less common sense? (the left-handed analogy was quite apt.)

-William

On 4/3/2013 5:50 PM, Jed Wesley-Smith wrote:

On 3 April 2013 22:36, Stephen Colebourne <scolebourne at joda.org> wrote:

It didn't come up in the Devoxx lab, but I found the filter() method confusing when reading code in the talks. It was not obvious to me whether it was filtering in or out.

I was then surprised that there was only one method in the API for filtering, rather than two - one to remove and one to retain. While clearly they are a logical not, in code readbility terms its typically a lot clearer. Perhaps keep() and reject()? I'm sure there are other names, but filter alone feels very unclear. (I can't remember which it is now). Haskell: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-List.html#v:filter Scala: http://www.scala-lang.org/api/current/index.html#scala.collection.immutable.List Standard ML: http://www.standardml.org/Basis/list.html#SIG:LIST.filter:VAL Erlang: http://www.erlang.org/doc/man/lists.html#filter-2 Guava: http://docs.guava-libraries.googlecode.com/git/javadoc/com/google/common/collect/Iterables.html#filter(java.lang.Iterable, com.google.common.base.Predicate) Wikipedia: http://en.wikipedia.org/wiki/Filter(higher-orderfunction) all define the same behaviour and name of this method. It is sufficiently commonplace that to define it differently would be arbitrary and random. cheers, jed.

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