Array Opcodes

Array Opcodes

Variable Name

An array must be created (via init or fillarray) as kMyName plus ending brackets. The brackets determine the dimensions of the array. So,

kArr[] init 10

creates a one-dimensional array of length 10, whereas

kArr[][] init 10, 10

creates a two-dimensional array with 10 rows and 10 columns.

After the initalization of the array, referring to the array as a whole is done without any brackets. Brackets are only used if an element is indexed:

kArr[]   init 10             ;with brackets because of initialization
kLen     = lenarray(kArr)    ;without brackets
kFirstEl = kArr[0]           ;indexing with brackets

The same syntax is used for a simple copy via the '=' operator:

kArr1[] fillarray 1, 2, 3, 4, 5
kArr2[] = kArr1              ;creates kArr2 as copy of kArr1

k-rate

Note that most array operations are currently k-rate only. So like any other k-rate opcode, an operation on arrays will be automatically repeated every k-cycle. For instance, this code will repeat re-writing the array with different random values every k-cycle, as long as the instrument runs:

kArr[] init 10
kIndx  = 0
until kIndx == lenarray(kArr) do
  kArr[kIndx] rnd31 10, 0
  kIndx += 1
od

If you want to avoid this, you must organize it in one of the usual ways, for instance by using a trigger:

kArr[] init 10
kTrig metro 1
if kTrig == 1 then ;do the following once a second
  kIndx  = 0
  until kIndx == lenarray(kArr) do
    kArr[kIndx] rnd31 10, 0
    kIndx += 1
  od
endif

Creation/Initialization

The usual way to create an array is with init:

kArr[]   init 10     ;creates one-dimensional array with length 10
kArr[][] init 10, 10 ;creates two-dimensional array

A one-dimensional array can also be created and filled with distinct values by the opcode fillarray. This line creates a vector with length 4 and puts in the numbers [1, 2, 3, 4]:

kArr[] fillarray 1, 2, 3, 4

Length

The function lenarray(kArr) reports the length of an array. See example for function lenarray.

Copy Arrays to/from Tables

copyf2array kArr, kfn

copies data from an ftable to a vector.

copya2ftab kArr, kfn

copies data from a vector to an function table.

See examples for opcodes copyf2array and copya2ftab.

Array Operations: Math

+, -, *, / on a Number

If the four basic math operators are used between an array and a scalar (number), the operation is applied to each element. The safest way to do this is to store the result in a new array:

kArr1[] fillarray 1, 2, 3
kArr2[] = kArr1 + 10    ;(kArr2 is now [11, 12, 13])

Here is an example of array/scalar operations. It uses the file array_scalar_math.csd.

Example 3. Example of array operations

<CsoundSynthesizer>
<CsOptions>
-n -m128
</CsOptions>
<CsInstruments>


  instr 1

;create array and fill with numbers 1..10
kArr1[] fillarray 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

;print content
        printf  "%s", 1, "\nInitial content:\n"
kndx    =       0
  until kndx == lenarray(kArr1) do
        printf  "kArr[%d] = %f\n", kndx+1, kndx, kArr1[kndx]
kndx    +=      1
  od

;add 10
kArr2[] =       kArr1 + 10

;print content
        printf  "%s", 1, "\nAfter adding 10:\n"
kndx    =       0
  until kndx == lenarray(kArr2) do
        printf  "kArr[%d] = %f\n", kndx+1, kndx, kArr2[kndx]
kndx    +=      1
  od

;subtract 5
kArr3[] =       kArr2 - 5

;print content
        printf  "%s", 1, "\nAfter subtracting 5:\n"
kndx    =       0
  until kndx == lenarray(kArr3) do
        printf  "kArr[%d] = %f\n", kndx+1, kndx, kArr3[kndx]
kndx    +=      1
  od

;multiply by -1.5
kArr4[] =       kArr3 * -1.5

;print content
        printf  "%s", 1, "\nAfter multiplying by -1.5:\n"
kndx    =       0
  until kndx == lenarray(kArr4) do
        printf  "kArr[%d] = %f\n", kndx+1, kndx, kArr4[kndx]
kndx    +=      1
  od

;divide by -3/2
kArr5[] =       kArr4 / -(3/2)

;print content
        printf  "%s", 1, "\nAfter dividing by -3/2:\n"
kndx    =       0
  until kndx == lenarray(kArr5) do
        printf  "kArr[%d] = %f\n", kndx+1, kndx, kArr5[kndx]
kndx    +=      1
  od

;turnoff
        turnoff
  endin
  

</CsInstruments>
<CsScore>
i 1 0 .1
</CsScore>
</CsoundSynthesizer>


+, -, *, / on a Second Array

If the four basic math operators are used between two arrays, the operation is applied element by element. The result can be straightforward stored in a new array:

kArr1[] fillarray 1, 2, 3
kArr2[] fillarray 10, 20, 30
kArr3[] = kArr1 + kArr2    ;(kArr3 is now [11, 22, 33])

Here is an example of array operations. It uses the file array_array_math.csd.

Example 4. Example of array operations

<CsoundSynthesizer>
<CsOptions>
-n -m128
</CsOptions>
<CsInstruments>

  instr 1

;create array and fill with numbers 1..10 resp .1..1
kArr1[] fillarray 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
kArr2[] fillarray 1, 2, 3, 5, 8, 13, 21, 34, 55, 89

;print contents
        printf  "%s", 1, "\nkArr1:\n"
kndx    =       0
  until kndx == lenarray(kArr1) do
        printf  "kArr1[%d] =%f\n", kndx+1, kndx, kArr1[kndx]
kndx    +=      1
  od
        printf  "%s", 1, "\nkArr2:\n"
kndx    =       0
  until kndx == lenarray(kArr2) do
        printf  "kArr2[%d] = %f\n", kndx+1, kndx, kArr2[kndx]
kndx    +=      1
  od

;add arrays
kArr3[] =       kArr1 + kArr2

;print content
        printf  "%s", 1, "\nkArr1 + kArr2:\n"
kndx    =       0
  until kndx == lenarray(kArr3) do
        printf  "kArr3[%d] = %f\n", kndx+1, kndx, kArr3[kndx]
kndx    +=      1
  od

;subtract arrays
kArr4[] =       kArr1 - kArr2

;print content
        printf  "%s", 1, "\nkArr1 - kArr2:\n"
kndx    =       0
  until kndx == lenarray(kArr4) do
        printf  "kArr4[%d] = %f\n", kndx+1, kndx, kArr4[kndx]
kndx    +=      1
  od

;multiply arrays
kArr5[] =       kArr1 * kArr2

;print content
        printf  "%s", 1, "\nkArr1 * kArr2:\n"
kndx    =       0
  until kndx == lenarray(kArr5) do
        printf  "kArr5[%d] = %f\n", kndx+1, kndx, kArr5[kndx]
kndx += 1
  od

;divide arrays
kArr6[] =       kArr1 / kArr2

;print content
        printf  "%s", 1, "\nkArr1 / kArr2:\n"
kndx    =       0
  until kndx == lenarray(kArr6) do
        printf  "kArr5[%d] = %f\n", kndx+1, kndx, kArr6[kndx]
kndx += 1
  od

;turnoff
        turnoff
        
  endin
  
</CsInstruments>
<CsScore>
i 1 0 .1
</CsScore>
</CsoundSynthesizer>


Map a Function to an Array

kArrRes maparray kArrSrc, "fun"

maps the k-rate 1-arg function in the string to every element of the vector.

Possible functions are for instance abs, ceil, exp, floor, frac, int, log, log10, round, sqrt. This is a simple example:

kArrSrc[] fillarray 1, 2, 3, 4, 5
kArrRes[] init      5
kArrRes   maparray  kArrSrc, "sqrt"

See example for opcode maparray.

Array Operations: min, max, sum, scale, slice

Minimum and Maximum

  kMin [,kMinIndx] minarray kArr

returns the smallest value in an array, and optionally its index.

  kMax [,kMaxIndx] maxarray kArr

returns the largest value in an array, and optionally its index. See examples for opcodes minarray and maxarray.

Sum

  kSum sumarray kArr

returns the sum of all values in kArr. See example for opcode sumarray.

Scale

  scalearray kArr, kMin, kMax

scales all values in kArr between kMin and kMax.

  kArr[] fillarray  1, 3, 9, 5, 6
         scalearray kArr, 1, 3

changes kArr to [1, 1.5, 3, 2, 2.25]. See example for opcode scalearray.

Slice

  slicearray kArr, iStart, iEnd

returns a slice of kArr from index iStart to index iEnd (included).

The array for receiving the slice must have been created in advance:

  kArr[]  fillarray  1, 2, 3, 4, 5, 6, 7, 8, 9
  kArr1[] init       5
  kArr2[] init       4
  kArr1   slicearray kArr, 0, 4        ;[1, 2, 3, 4, 5]
  kArr2   slicearray kArr, 5, 8        ;[6, 7, 8, 9]

See example for opcode slicearray.

Arrays in UDOs

The dimension of an input array must be declared in two places:

  • as k[] or k[][] in the type input list
  • as kName[], kName[][] etc in the xin list.

For instance :

opcode FirstEl, k, k[]
;returns the first element of vector kArr
kArr[] xin
       xout   kArr[0]
endop

Here is an example of an array in an UDO. It uses the file array_udo.csd.

Example 5. Example of an array in an UDO

<CsoundSynthesizer>
<CsOptions>
-nm128
</CsOptions>
<CsInstruments>

  opcode FirstEl, k, k[]
  ;returns the first element of vector kArr
kArr[] xin
xout kArr[0]
  endop

  instr 1 
kArr[] fillarray 6, 3, 9, 5, 1
kFirst FirstEl kArr
printf "kFirst = %d\n", 1, kFirst
turnoff
  endin

</CsInstruments>
<CsScore>
i 1 0 .1
</CsScore>
</CsoundSynthesizer>


Credits

This manual page has been written by Joachim Heintz.
July 2013

New in Csound 6.00