tablefilteri
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## tablefilteri

tablefilteri — Filters a source table and writes result into a destination table.

## Description

This opcode can be used in order to filter values from function tables following certain algorithms. The filtered output is written into a destination table and the number of elements that have passed the filter is returned.

## Syntax

    inumpassed tablefilteri iouttable, iintatble, imode, iparam

## Initialization

inumpassed -- the number of elements that have passed the filter.

iouttable -- the number of the table containing the values that have passed.

iintatble -- the number of the table used as filter input.

imode -- mode of the filter:

- 1 -- tests the weight of the denominators of the fractions in the source table. Letting pass only values from the source that are less heavy than the weight of the threshold.
- 2 -- tests the weight of the denominators of the fractions in the source table. Letting pass only values from the source that are heavier than or equal to the weight of the threshold.

iparam -- integer threshold parameter for the filter. It means that denominators whose weights are heavier than the weight of this threshold are not passed through the filter. The weight of an integer is calculated using Clarence Barlow's function of indigestibility of a number. According to this function, higher prime numbers contribute to an increased weight of any natural integer they divide. The order of the first 16 integers according to their indigestibility is: 1, 2, 4, 3, 8, 6, 16, 12, 9, 5, 10, 15, 7, 14.

## Examples

Here is an example of the tablefilteri opcode. It uses the file tablefilter.csd.

Example 1027. Example of the tablefilteri opcode.

See the sections Real-time Audio and Command Line Flags for more information on using command line flags.

    <CsoundSynthesizer>
    <CsOptions>

    </CsOptions>
    <CsInstruments>

    sr=44100
    ksmps=10
    nchnls=1

          gifarn init 8     ; initialise integer for Farey Sequence F_8
          gires fareyleni gifarn  ; calculate length of F_8, returns 23
          ; the table length won't be a power of 2
          ; (The length of a Farey Sequence with n > 1 is always odd)
          gilen init gires * -1

          gifarey ftgen 200, 0, gilen, "farey", gifarn, 0

          ; initialize destiniation table with 0s
          gifiltered ftgen 0, 0, gilen, 21, 1, 0

          ; initialize second destiniation table with 0s
          gifiltered2 ftgen 0, 0, gilen, 21, 1, 0

          ; table filtering opcode:   dest.         source,         mode,   threshold
          ginumpassed tablefilteri    gifiltered,   gifarey,        1,      6
          ; the threshold parameter indicates that denominators whose weights are heavier
          ; than 6 are not passing through the filter. The weight is calculated using
          ; Clarence Barlow's function of indigestibility of a number. According to this function,
          ; higher prime numbers contribute to an increased weight of any natural integer they divide.
          ; ginumpassed is the number of elements from the source table 'gifarey'
          ; that have passed the test and which have been copied to the destination table 'gifiltered'

          ; apply a different filter:
          ginumpassed2 tablefilteri   gifiltered2,  gifarey,        2,      5
          ; In mode=2 we again test the digestibility of the denominators of the
          ; fractions in the source table.
          ; The difference to mode=1 is that we now let pass only vaules from the
          ; source that are as heavy as the threshold or greater.

    instr 4
          kndx init 0 ; read out elements of now filtered F_8 sequentially and print to file
          if (kndx < ginumpassed) then
             kelem tab kndx, gifiltered
             fprintks "fareyfilter_lp.txt", "%2.6f\\n", kelem
             kndx = kndx+1
          endif
    endin

    instr 5
          kndx init 0 ; read out elements and print to file
          if (kndx < ginumpassed2) then
             kelem tab kndx, gifiltered2
             fprintks "fareyfilter_hp.txt", "%2.6f\\n", kelem
             kndx = kndx+1
          endif
    endin

    </CsInstruments>
    <CsScore>

    i4      0     1
    i5      0     1
    e
    </CsScore>
    </CsoundSynthesizer>

## Credits

Author: Georg Boenn
University of Glamorgan, UK

New in Csound version 5.13

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