Package org.apache.lucene.util.fst

Class Util

java.lang.Object
org.apache.lucene.util.fst.Util
public final class Util extends Object
Static helper methods.

  • Constructor Details

    • Util

      private Util()

  • Method Details

    • get

      public static <T> T get(FST<T> fst, IntsRef input) throws IOException
      Looks up the output for this input, or null if the input is not accepted.
      Throws:
      IOException

    • get

      public static <T> T get(FST<T> fst, BytesRef input) throws IOException
      Looks up the output for this input, or null if the input is not accepted
      Throws:
      IOException

    • getByOutput

      @Deprecated public static IntsRef getByOutput(FST<Long> fst, long targetOutput) throws IOException
      Deprecated.
      Reverse lookup (lookup by output instead of by input), in the special case when your FSTs outputs are strictly ascending. This locates the input/output pair where the output is equal to the target, and will return null if that output does not exist.

      NOTE: this only works with FST<Long>, only works when the outputs are ascending in order with the inputs. For example, simple ordinals (0, 1, 2, ...), or file offsets (when appending to a file) fit this.

      Throws:
      IOException

    • getByOutput

      @Deprecated public static IntsRef getByOutput(FST<Long> fst, long targetOutput, FST.BytesReader in, FST.Arc<Long> arc, FST.Arc<Long> scratchArc, IntsRefBuilder result) throws IOException
      Deprecated.
      Expert: like getByOutput(FST, long) except reusing BytesReader, initial and scratch Arc, and result.
      Throws:
      IOException

    • shortestPaths

      public static <T> Util.TopResults<T> shortestPaths(FST<T> fst, FST.Arc<T> fromNode, T startOutput, Comparator<T> comparator, int topN, boolean allowEmptyString) throws IOException
      Starting from node, find the top N min cost completions to a final node.
      Throws:
      IOException

    • toDot

      public static <T> void toDot(FST<T> fst, Writer out, boolean sameRank, boolean labelStates) throws IOException
      Dumps an FST to a GraphViz's dot language description for visualization. Example of use: 
       PrintWriter pw = new PrintWriter("out.dot");
 Util.toDot(fst, pw, true, true);
 pw.close();
      and then, from command line: 
       dot -Tpng -o out.png out.dot

      Note: larger FSTs (a few thousand nodes) won't even render, don't bother.

      Parameters:
      sameRank - If true, the resulting dot file will try to order states in layers of breadth-first traversal. This may mess up arcs, but makes the output FST's structure a bit clearer.
      labelStates - If true states will have labels equal to their offsets in their binary format. Expands the graph considerably.
      Throws:
      IOException
      See Also:

    • emitDotState

      private static void emitDotState(Writer out, String name, String shape, String color, String label) throws IOException
      Emit a single state in the dot language.
      Throws:
      IOException

    • printableLabel

      private static String printableLabel(int label)
      Ensures an arc's label is indeed printable (dot uses US-ASCII).

    • toUTF16

      public static IntsRef toUTF16(CharSequence s, IntsRefBuilder scratch)
      Just maps each UTF16 unit (char) to the ints in an IntsRef.

    • toUTF32

      public static IntsRef toUTF32(CharSequence s, IntsRefBuilder scratch)
      Decodes the Unicode codepoints from the provided CharSequence and places them in the provided scratch IntsRef, which must not be null, returning it.

    • toUTF32

      public static IntsRef toUTF32(char[] s, int offset, int length, IntsRefBuilder scratch)
      Decodes the Unicode codepoints from the provided char[] and places them in the provided scratch IntsRef, which must not be null, returning it.

    • toIntsRef

      public static IntsRef toIntsRef(BytesRef input, IntsRefBuilder scratch)
      Just takes unsigned byte values from the BytesRef and converts into an IntsRef.

    • toBytesRef

      public static BytesRef toBytesRef(IntsRef input, BytesRefBuilder scratch)
      Just converts IntsRef to BytesRef; you must ensure the int values fit into a byte.

    • readCeilArc

      public static <T> FST.Arc<T> readCeilArc(int label, FST<T> fst, FST.Arc<T> follow, FST.Arc<T> arc, FST.BytesReader in) throws IOException
      Reads the first arc greater or equal than the given label into the provided arc in place and returns it iff found, otherwise return null.
      Parameters:
      label - the label to ceil on
      fst - the fst to operate on
      follow - the arc to follow reading the label from
      arc - the arc to read into in place
      in - the fst's FST.BytesReader
      Throws:
      IOException

    • binarySearch

      static <T> int binarySearch(FST<T> fst, FST.Arc<T> arc, int targetLabel) throws IOException
      Perform a binary search of Arcs encoded as a packed array
      Type Parameters:
      T - the output type of the FST
      Parameters:
      fst - the FST from which to read
      arc - the starting arc; sibling arcs greater than this will be searched. Usually the first arc in the array.
      targetLabel - the label to search for
      Returns:
      the index of the Arc having the target label, or if no Arc has the matching label, -1 - idx), where idx is the index of the Arc with the next highest label, or the total number of arcs if the target label exceeds the maximum.
      Throws:
      IOException - when the FST reader does