**filter** -text -package

filter, applied to a predicate and a list, returns the list of those elements that satisfy the predicate; i.e.,
> filter p xs = [ x | x <- xs, p x]
*O(n)* filter, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate.
*O(n)*. Filter all elements that satisfy some predicate.

*O(n)* filter, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate.
*O(n)* filter, applied to a predicate and a ByteString, returns a ByteString containing those characters that satisfy the predicate. This function is subject to array fusion.
*O(n)*. Filter all values that satisfy some predicate.
> filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
> filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty
> filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty

*O(n)*. Filter all values that satisfy the predicate.
> filter (> "a") (fromList [(5,"a"), (3,"b")]) == singleton 3 "b"
> filter (> "x") (fromList [(5,"a"), (3,"b")]) == empty
> filter (< "a") (fromList [(5,"a"), (3,"b")]) == empty

*O(n)*. The filter function takes a predicate p and a sequence xs and returns a sequence of those elements which satisfy the predicate.
*O(n)*. Filter all elements that satisfy the predicate.

This generalizes the list-based filter function.
Use the filtered compression strategy for data produced by a filter (or predictor). Filtered data consists mostly of small values with a somewhat random distribution. In this case, the compression algorithm is tuned to compress them better. The effect of this strategy is to force more Huffman coding and less string matching; it is somewhat intermediate between defaultCompressionStrategy and huffmanOnlyCompressionStrategy.

*O(n)*. Filter all keys/values that satisfy some predicate.
> filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"

*O(n)*. Filter all keys/values that satisfy the predicate.
> filterWithKey (\k _ -> k > 4) (fromList [(5,"a"), (3,"b")]) == singleton 5 "a"

*Deprecated: Use filteredStrategy. CompressionStrategy constructors will be hidden in version 0.7 *

Direct MonadPlus equivalent of filter filter = (mfilter:: (a -> Bool) -> [a] -> [a] applicable to any MonadPlus, for example mfilter odd (Just 1) == Just 1 mfilter odd (Just 2) == Nothing
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