filter (redirected from x-ray filter)

filter

(1) To select data. Filters use patterns (masks) against which all data are compared and only matching data are "passed through," hence the concept of a filter. For example, e-mail clients and servers can look for messages with text patterns that are recognized as spam and delete them. An e-mail client can be set up to filter messages and store them in separate mailboxes as a way of organizing the mail, or it can be set to alert the user when a certain type of message arrives. See Bayesian filtering and spam filter.

(2) To change data. In this usage of the term, the concept of a filter (a pass-through device) is less obvious, but nevertheless widely used. For example, a sort routine changes the sequence of data. A conversion routine (import or export filter) changes one type of data, text or graphics format into another. See image filter and parse.

(3) See packet filter.

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filter

1. a porous substance, such as paper or sand, that allows fluid to pass but retains suspended solid particles: used to clean fluids or collect solid particles

2. any device containing such a porous substance for separating suspensions from fluids

3. any of various porous substances built into the mouth end of a cigarette or cigar for absorbing impurities such as tar

4. any electronic, optical, or acoustic device that blocks signals or radiations of certain frequencies while allowing others to pass

5. any transparent disc of gelatine or glass used to eliminate or reduce the intensity of given frequencies from the light leaving a lamp, entering a camera, etc.

6. Brit a traffic signal at a road junction consisting of a green arrow which when illuminated permits vehicles to turn either left or right when the main signals are red

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1.		filter - (Originally Unix, now also MS-DOS) A program that processes an input data stream into an output data stream in some well-defined way, and does no I/O to anywhere else except possibly on error conditions; one designed to be used as a stage in a pipeline (see plumbing). Compare sponge.
2.		filter - (functional programming) A higher-order function which takes a predicate and a list and returns those elements of the list for which the predicate is true. In Haskell: filter p [] = [] filter p (x:xs) = if p x then x : rest else rest where rest = filter p xs See also filter promotion.