PureBasic Forums - English

Posted: **Tue Dec 26, 2017 8:39 am**

I have a huge SQLite database with the following fields: id, date, type, result

Regrettably, the native aggregate functions have no percentile function, so I bypass this with the following SQL-statement.

For example to get the 90th percentile of all results with type=3:

Code: Select all

SELECT result AS 'type3_percent90'
FROM table
WHERE type=3
ORDER BY result ASC
LIMIT 1
OFFSET (SELECT
         COUNT(*)
        FROM table
        WHERE type=3) * 9 / 10 - 1;

This is ok for single queries, but not for complex requests, so it would be better to have an implemented function.

Could anybody help how to convert the percentile extension into PB ?

TX a lot,
Oliver

Posted: **Tue Dec 26, 2017 1:20 pm**

Hi,

don't know how to test it, so I don't know if it works 100% correct.

Code: Select all

CompilerIf #PB_Compiler_IsMainFile
  EnableExplicit
CompilerEndIf

ImportC ""
  qsort(*base, nitems.l, size.l, *Prog)
  ;qsort(void *base, size_t nitems, size_t size, Int (*compar)(const void *, const void*))
EndImport

CompilerSelect #PB_Compiler_OS
  CompilerCase #PB_OS_MacOS
    ImportC "/Applications/PureBasic/purelibraries/macos/libraries/libpbsqlite3.a" 
  CompilerDefault  
    ImportC "sqlite3.lib" 
CompilerEndSelect
  
  sqlite3_create_function(DatabaseID, zFunctionName.p-utf8, nArg.l, eTextRep.l, *pApp, *xFunc, *xStep, *xFinal)
  sqlite3_aggregate_context(*sqlite3_context, nBytes.l)
  sqlite3_result_double(*sqlite3_context, dbl.d)
  sqlite3_value_numeric_type.l(*sqlite3_value)
  sqlite3_value_double.d(*sqlite3_value)
  sqlite3_value_int.i(*sqlite3_value)
  
  sqlite3_value_type.i(*sqlite3_value)
  
  sqlite3_realloc(*void, int.l)
  sqlite3_free(*void)
  
  sqlite3_result_error(*sqlite3_context, char.p-utf8, int.l)
  sqlite3_result_error_nomem(*sqlite3_context)
  
  sqlite3_errcode.i(*db)
  sqlite3_errmsg16.i(*sqlite3)
EndImport 

#SQLITE_OK = 0

#SQLITE_UTF8 = 1


#SQLITE_INTEGER = 1
#SQLITE_FLOAT = 2
#SQLITE3_TEXT = 3
#SQLITE_BLOB = 4
#SQLITE_NULL = 5



Structure PercentileStrucure
  nAlloc.i    ; Number of slots allocated for a[]
  nUsed.i     ; Number of slots actually used in a[]
  rPct.d      ; 1.0 more than the value for P
  *a.Double   ; Array of Y values
EndStructure



Procedure.i sameValue(a.d, b.d)
  a - b
  ProcedureReturn Bool(a >= -0.001 And a <= 0.001)
EndProcedure




ProcedureC percentStep(*pCtx, argc.l, *argv)
  
  Protected *ptr, *a
  Protected *p.PercentileStrucure
  Protected.d rPct
  Protected.i eType
  Protected.d y
  Protected.i n
  
  
  ; Requirement 3:  P must be a number between 0 And 100
  *ptr = PeekI(*argv + 1 * SizeOf(Long))
  eType = sqlite3_value_numeric_type(*ptr)
  rPct = sqlite3_value_double(*ptr);
  
  If (eType <> #SQLITE_INTEGER And eType <> #SQLITE_FLOAT) Or (rPct < 0.0 Or rPct > 100.0)
    sqlite3_result_error(*pCtx, "2nd argument to percentile() is not a number between 0.0 And 100.0", -1)
    ProcedureReturn
  EndIf
  
  
  ; Allocate the session context.
  *p = sqlite3_aggregate_context(*pCtx, SizeOf(PercentileStrucure))
  If *p = 0 
    ProcedureReturn
  EndIf

  ; Remember the P value.  Throw an error If the P value is different
  ; from any prior row, per Requirement (2).
  If *p\rPct = 0.0
    *p\rPct = rPct + 1.0
  ElseIf Not sameValue(*p\rPct, rPct + 1.0)
    sqlite3_result_error(*pCtx, "2nd argument to percentile() is not the same For all input rows", -1)
    ProcedureReturn
  EndIf
  
  ; Ignore rows For which Y is NULL
  *ptr = PeekI(*argv + 0 * SizeOf(Long))
  eType = sqlite3_value_type(*ptr)
  If eType = #SQLITE_NULL
    ProcedureReturn
  EndIf
  
  ; If Not NULL, then Y must be numeric.  Otherwise throw an error.
  ; Requirement 4
  If eType <> #SQLITE_INTEGER And eType <> #SQLITE_FLOAT
    sqlite3_result_error(*pCtx, "1st argument to percentile() is not numeric", -1)
    ProcedureReturn
  EndIf
  
  ; Throw an error If the Y value is infinity Or NaN
  y = sqlite3_value_double(*ptr)
  If IsInfinity(y)
    sqlite3_result_error(*pCtx, "Inf input to percentile()", -1)
    ProcedureReturn
  EndIf
  
  ; Allocate And store the Y
  If *p\nUsed >= *p\nAlloc
    n = *p\nAlloc * 2 + 250
    *a = sqlite3_realloc(*p\a, 8 * n)
    If *a = 0
      sqlite3_free(*p\a)
      ClearStructure(*p, PercentileStrucure)
      sqlite3_result_error_nomem(*pCtx)
      ProcedureReturn
    EndIf
    *p\nAlloc = n
    *p\a = *a
  EndIf
  ;*p\a[*p\nUsed] = y
  PokeD(*p\a + 8 * *p\nUsed, y)
  *p\nUsed + 1
  
EndProcedure



ProcedureC.l doubleCmp(*pA, *pB)
  
  Protected Result.l
  Protected.d a, b
  
  Result = 1
  
  a = PeekD(*pA)
  b = PeekD(*pB)
  If a=b
    Result = 0
  ElseIf a < b
    Result = -1
  EndIf
  
  ProcedureReturn Result
  
EndProcedure



ProcedureC percentFinal(*pCtx)
  
  Protected *p.PercentileStrucure
  Protected.i i1, i2
  Protected.d v1, v2
  Protected.d ix, vx
  Protected.i i
  
  
  *p = sqlite3_aggregate_context(*pCtx, 0)
  If *p
    If *p\a <> 0
      If  *p\nUsed
        
        qsort(*p\a, *p\nUsed, SizeOf(double), @doubleCmp())
;         For i = 0 To *p\nUsed - 2
;           Debug PeekD(*p\a + 8 * i)
;         Next i
        
        
        
;         Dim a.d(*p\nUsed - 1)
;         
;         For i = 0 To *p\nUsed - 1
;           ;a(i) = *p\a[i]
;           a(i) = PeekD(*p\a + 8 * i)
;         Next i
;         
;         SortArray(a(), #PB_Sort_Ascending, 0, ArraySize(a()))
;         Debug "-----"
;         For i = 0 To ArraySize(a())
;           Debug a(i)
;         Next i
;         Debug "+++++"
        
        ix = (*p\rPct - 1.0) * (*p\nUsed - 1) * 0.01
        i1 = ix
        ;i2 = ix==(double)i1 || i1==p->nUsed-1 ? i1 : i1+1
        If ix = i1
          i2 = i1
        Else
          If i1 = *p\nUsed - 1
            i2 = i1
          Else
            i2 = i1 + 1
          EndIf
        EndIf
        ;v1 = *p\a[i1]
        v1 = PeekD(*p\a + 8 * i1)
        ;v1 = a(i1)
        ;v2 = *p\a[i2]
        v2 = PeekD(*p\a + 8 * i2)
        ;v2 = a(i2)
        vx = v1 + (v2 - v1) * (ix - i1)
        sqlite3_result_double(*pCtx, vx)
      EndIf
      
      sqlite3_free(*p\a)
    EndIf
    ClearStructure(*p, PercentileStrucure)
  EndIf
  
EndProcedure


Procedure.i sqlite3_percentile_init(db.i)
  
  ProcedureReturn Bool(sqlite3_create_function(DatabaseID(db), "percentile", 2, #SQLITE_UTF8, 0, 0, @percentStep(), @percentFinal()) = #SQLITE_OK)
  
EndProcedure


CompilerIf #PB_Compiler_IsMainFile
  
  Define.i DB, i, j
  
  
  UseSQLiteDatabase()
  
  DB = OpenDatabase(#PB_Any, ":memory:", "", "")
  If DB
    
    If sqlite3_percentile_init(DB)
      
      DatabaseUpdate(DB, "CREATE TABLE test(a INTEGER)")
      
      For i = 0 To 10
        j = Random(1000)
        Debug Str(i) + ": " + Str(j)
        DatabaseUpdate(DB, "INSERT INTO test VALUES (" + Str(j) + ")")
      Next i
      
      If DatabaseQuery(DB, "SELECT percentile(a, 50) FROM test")
        While NextDatabaseRow(DB)
          Debug GetDatabaseString(DB, 0)
        Wend
        FinishDatabaseQuery(DB)
        If sqlite3_errcode(DatabaseID(DB))
          Debug PeekS(sqlite3_errmsg16(DatabaseID(DB)))
        EndIf
      Else
        Debug DatabaseError()
      EndIf
      
    EndIf
    
    CloseDatabase(DB)
  EndIf
  
CompilerEndIf

Bernd

Posted: **Tue Dec 26, 2017 1:29 pm**

Ups...

I think it does not work.
It returns the value at the coressponding row.

I modified the listing above to show this.

Bernd

Posted: **Tue Dec 26, 2017 1:42 pm**

Seems to work now.

But I want to eliminate my additional array which was needed because I was not able to define the variable double array
inside of the structure [0] failed at allocation.

Bernd

Posted: **Tue Dec 26, 2017 1:52 pm**

Hope it works now without my additional array.

Extensive testing is needed!

Bernd

Posted: **Tue Dec 26, 2017 4:00 pm**

Hi Bernd,
great, thank you very much !

But there is still a bug; I modified the sample:
For example with percentile=10, the function returns 9.9, but should return 9.0

Code: Select all

CompilerIf #PB_Compiler_IsMainFile
 
  Define.i DB, i, j
  UseSQLiteDatabase()
  DB = OpenDatabase(#PB_Any, ":memory:", "", "")
  If DB
    If sqlite3_percentile_init(DB)
      DatabaseUpdate(DB, "CREATE TABLE test(a DOUBLE)")
      For i = 0 To 99
        j = i; fill with 0-99
        DatabaseUpdate(DB, "INSERT INTO test VALUES (" + Str(j) + ")")
      Next i
    ; show all records
      If DatabaseQuery(DB, "SELECT * FROM test ORDER BY a ASC")
        While NextDatabaseRow(db)
        Debug GetDatabaseString(db,0)  
        Wend
        FinishDatabaseQuery(db)
      EndIf
      For i=0 To 10
      Debug Str(i*10)+" percentile"
      If DatabaseQuery(DB, "SELECT a  FROM test ORDER BY a ASC LIMIT 1 OFFSET (Select COUNT(*) FROM test) *"+Str(i)+" / 10 - 1")
        If NextDatabaseRow(DB)
          Debug "SQL:"+GetDatabaseString(DB, 0)
        EndIf
        FinishDatabaseQuery(DB)
      Else
        If sqlite3_errcode(DatabaseID(DB))
          Debug PeekS(sqlite3_errmsg16(DatabaseID(DB)))
        EndIf
      EndIf
      If DatabaseQuery(DB, "SELECT percentile(a, "+Str(i*10)+") from test")
        While NextDatabaseRow(DB)
          Debug "External:"+GetDatabaseString(DB, 0)
        Wend
        FinishDatabaseQuery(DB)
      Else
        If sqlite3_errcode(DatabaseID(DB))
          Debug PeekS(sqlite3_errmsg16(DatabaseID(DB)))
        EndIf
      EndIf
       Next       
    EndIf
    CloseDatabase(DB)
  EndIf
 CompilerEndIf

Any idea ? Thx a lot
Oliver

Posted: **Tue Dec 26, 2017 4:14 pm**

Hm...
I think you SQL select is a bit wrong.

If i is 0 you use an offset of -1. This can't be valid.

Posted: **Tue Dec 26, 2017 4:26 pm**

If I use the values of

https://onlinecourses.science.psu.edu/stat414/node/315

for the urban city, I get 53.8 as result. (instead of 53.6, which maybe a rounding issue)

Code: Select all

CompilerIf #PB_Compiler_IsMainFile
  
  Define.i DB, i, j
  
  
  UseSQLiteDatabase()
  
  DB = OpenDatabase(#PB_Any, ":memory:", "", "")
  If DB
    
    If sqlite3_percentile_init(DB)
      
      DatabaseUpdate(DB, "CREATE TABLE test(a INTEGER)")
      
;       For i = 0 To 10
;         j = Random(1000)
;         Debug Str(i) + ": " + Str(j)
;         DatabaseUpdate(DB, "INSERT INTO test VALUES (" + Str(j) + ")")
;       Next i
      
      DatabaseUpdate(DB, "INSERT INTO test VALUES (40)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (48)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (49)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (50)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (53)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (54)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (55)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (61)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (64)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (65)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (66)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (75)")
      DatabaseUpdate(DB, "INSERT INTO test VALUES (98)")
      
      
      If DatabaseQuery(DB, "SELECT percentile(a, 40) FROM test")
        While NextDatabaseRow(DB)
          Debug GetDatabaseString(DB, 0)
          Debug GetDatabaseString(DB, 1)
        Wend
        FinishDatabaseQuery(DB)
        If sqlite3_errcode(DatabaseID(DB))
          Debug PeekS(sqlite3_errmsg16(DatabaseID(DB)))
        EndIf
      Else
        Debug DatabaseError()
      EndIf
      
    EndIf
    
    CloseDatabase(DB)
  EndIf
  
CompilerEndIf

Posted: **Tue Dec 26, 2017 4:30 pm**

I can only say: I have translated the C example to PB.

In my opinion it is correct.
But maybe you can find a difference.

Posted: **Tue Dec 26, 2017 5:27 pm**

infratec wrote:If I use the values of https://onlinecourses.science.psu.edu/stat414/node/315 for the urban city, I get 53.8 as result. (instead of 53.6, which maybe a rounding issue)

MS Excel, (=PERCENTILE(A1:A13, 0.40)), returns 53.8.

Posted: **Tue Dec 26, 2017 6:10 pm**

After reading a bit more ...

There is no standard definition of percentile.

The Wiki shows different methods which results in 3 dfferent results:

1. The nearest rank method
Only values included in the values can be returned.

2. linear interpolation between closest ranks method
Has 3 defined possibilites: C= 1/2 C=0 and C=1

All of them results in different results.

So please tell me what you want ?

As mentioned: if you have enough values the results get closer.

Also MS Excel changed the method between some versions.

Bernd

Posted: **Tue Dec 26, 2017 7:00 pm**

infratec wrote:After reading a bit more ...

There is no standard definition of percentile.

The Wiki shows different methods which results in 3 dfferent results:

1. The nearest rank method
Only values included in the values can be returned.

Sorry, my skills in statistics are very poor and I only knew the nearest rank method..
The result need to be a member of the values list
So it is method 1..

TIA
Oliver

Posted: **Tue Dec 26, 2017 10:14 pm**

Hi,

percentile nearest rank methode

see:
https://en.wikipedia.org/wiki/Percentile

Code: Select all

CompilerIf #PB_Compiler_IsMainFile
  EnableExplicit
CompilerEndIf

ImportC ""
  qsort(*base, nitems.l, size.l, *Prog)
  ;qsort(void *base, size_t nitems, size_t size, Int (*compar)(const void *, const void*))
EndImport

CompilerSelect #PB_Compiler_OS
  CompilerCase #PB_OS_MacOS
    ImportC "/Applications/PureBasic/purelibraries/macos/libraries/libpbsqlite3.a" 
    CompilerDefault  
      ImportC "sqlite3.lib" 
    CompilerEndSelect
    
    sqlite3_create_function(DatabaseID, zFunctionName.p-utf8, nArg.l, eTextRep.l, *pApp, *xFunc, *xStep, *xFinal)
    sqlite3_aggregate_context(*sqlite3_context, nBytes.l)
    sqlite3_result_double(*sqlite3_context, dbl.d)
    sqlite3_value_numeric_type.l(*sqlite3_value)
    sqlite3_value_double.d(*sqlite3_value)
    
    sqlite3_value_type.i(*sqlite3_value)
    
    sqlite3_realloc(*void, int.l)
    sqlite3_free(*void)
    
    sqlite3_result_error(*sqlite3_context, char.p-utf8, int.l)
    sqlite3_result_error_nomem(*sqlite3_context)
    
    sqlite3_errcode.i(*db)
    sqlite3_errmsg16.i(*sqlite3)
  EndImport 
  
  #SQLITE_OK = 0
  
  #SQLITE_UTF8 = 1
  
  
  #SQLITE_INTEGER = 1
  #SQLITE_FLOAT = 2
  #SQLITE3_TEXT = 3
  #SQLITE_BLOB = 4
  #SQLITE_NULL = 5
  
  
  
  Structure Percentile
    nAlloc.i    ; Number of slots allocated for a[]
    nUsed.i     ; Number of slots actually used in a[]
    rPct.d      ; 1.0 more than the value for P
    *a.Double   ; Array of Y values
  EndStructure
  
  
  
  Procedure.i sameValue(a.d, b.d)
    a - b
    ProcedureReturn Bool(a >= -0.001 And a <= 0.001)
  EndProcedure
  
  
  
  
  ProcedureC percentStep(*pCtx, argc.l, *argv)
    
    Protected *ptr, *a
    Protected *p.Percentile
    Protected.d rPct
    Protected.i eType
    Protected.d y
    Protected.i n
    
    
    ; Requirement 3:  P must be a number between 0 And 100
    *ptr = PeekI(*argv + 1 * SizeOf(Long))
    eType = sqlite3_value_numeric_type(*ptr)
    rPct = sqlite3_value_double(*ptr);
    
    If (eType <> #SQLITE_INTEGER And eType <> #SQLITE_FLOAT) Or (rPct < 0.0 Or rPct > 100.0)
      sqlite3_result_error(*pCtx, "2nd argument to percentile() is not a number between 0.0 And 100.0", -1)
      ProcedureReturn
    EndIf
    
    
    ; Allocate the session context.
    *p = sqlite3_aggregate_context(*pCtx, SizeOf(Percentile))
    If *p = 0 
      ProcedureReturn
    EndIf
    
    ; Remember the P value.  Throw an error If the P value is different
    ; from any prior row, per Requirement (2).
    If *p\rPct = 0.0
      *p\rPct = rPct; + 1.0
    ElseIf Not sameValue(*p\rPct, rPct); + 1.0)
      sqlite3_result_error(*pCtx, "2nd argument to percentile() is not the same For all input rows", -1)
      ProcedureReturn
    EndIf
    
    ; Ignore rows For which Y is NULL
    *ptr = PeekI(*argv + 0 * SizeOf(Long))
    eType = sqlite3_value_type(*ptr)
    If eType = #SQLITE_NULL
      ProcedureReturn
    EndIf
    
    ; If Not NULL, then Y must be numeric.  Otherwise throw an error.
    ; Requirement 4
    If eType <> #SQLITE_INTEGER And eType <> #SQLITE_FLOAT
      sqlite3_result_error(*pCtx, "1st argument to percentile() is not numeric", -1)
      ProcedureReturn
    EndIf
    
    ; Throw an error If the Y value is infinity Or NaN
    y = sqlite3_value_double(*ptr)
    If IsInfinity(y)
      sqlite3_result_error(*pCtx, "Inf input to percentile()", -1)
      ProcedureReturn
    EndIf
    
    ; Allocate And store the Y
    If *p\nUsed >= *p\nAlloc
      n = *p\nAlloc * 2 + 250
      *a = sqlite3_realloc(*p\a, 8 * n)
      If *a = 0
        sqlite3_free(*p\a)
        ClearStructure(*p, Percentile)
        sqlite3_result_error_nomem(*pCtx)
        ProcedureReturn
      EndIf
      *p\nAlloc = n
      *p\a = *a
    EndIf
    ;*p\a[*p\nUsed] = y
    PokeD(*p\a + 8 * *p\nUsed, y)
    *p\nUsed + 1
    
  EndProcedure
  
  
  
  ProcedureC.l doubleCmp(*pA.Double, *pB.Double)
    
    Protected Result.l
    
    Result = 1
    
    If *pA\d = *pB\d
      Result = 0
    ElseIf *pA\d < *pB\d
      Result = -1
    EndIf
    
    ProcedureReturn Result
    
  EndProcedure
  
  
  
  ProcedureC percentFinal(*pCtx)
    
    Protected *p.Percentile
    Protected.i i1, i2
    Protected.d v1, v2
    Protected.d ix, vx
    Protected.i i
    Protected.d v11, v22
    
    
    *p = sqlite3_aggregate_context(*pCtx, 0)
    If *p
      If *p\a <> 0
        If *p\nUsed
          
          If *p\rPct > 0
            If *p\rPct = 100
              vx = PeekD(*p\a + 8 * (*p\nUsed - 1))
            Else
              
              qsort(*p\a, *p\nUsed, SizeOf(double), @doubleCmp())
              ;         Debug "-----"
              ;         For i = 0 To *p\nUsed - 1
              ;           Debug Str(i) + ": " + StrD(PeekD(*p\a + 8 * i))
              ;         Next i
              ;         Debug "+++++"
              
              i1 = Round(*p\rPct / 100 * *p\nUsed, #PB_Round_Up) - 1
              
              vx = PeekD(*p\a + 8 * i1)
              
            EndIf
            
          Else
            vx = 0
          EndIf
          
          sqlite3_result_double(*pCtx, vx)
        EndIf
        
        sqlite3_free(*p\a)
      EndIf
      ClearStructure(*p, Percentile)
    EndIf
    
  EndProcedure
  
  
  Procedure.i sqlite3_percentile_init(db.i)
    
    ProcedureReturn Bool(sqlite3_create_function(DatabaseID(db), "percentile", 2, #SQLITE_UTF8, 0, 0, @percentStep(), @percentFinal()) = #SQLITE_OK)
    
  EndProcedure
  
  
  CompilerIf #PB_Compiler_IsMainFile
    
    Define.i DB, i, j
    
    
    UseSQLiteDatabase()
    
    DB = OpenDatabase(#PB_Any, ":memory:", "", "")
    If DB
      
      If sqlite3_percentile_init(DB)
        
        DatabaseUpdate(DB, "CREATE TABLE test(a INTEGER)")
        
        DatabaseUpdate(DB, "INSERT INTO test VALUES (15)")
        DatabaseUpdate(DB, "INSERT INTO test VALUES (20)")
        DatabaseUpdate(DB, "INSERT INTO test VALUES (35)")
        DatabaseUpdate(DB, "INSERT INTO test VALUES (40)")
        DatabaseUpdate(DB, "INSERT INTO test VALUES (50)")
        
        If DatabaseQuery(DB, "SELECT percentile(a, 50) FROM test")
          While NextDatabaseRow(DB)
            Debug "Res: " + GetDatabaseString(DB, 0)
          Wend
          FinishDatabaseQuery(DB)
          If sqlite3_errcode(DatabaseID(DB))
            Debug PeekS(sqlite3_errmsg16(DatabaseID(DB)))
          EndIf
        Else
          Debug DatabaseError()
        EndIf
        
      EndIf
      
      CloseDatabase(DB)
    EndIf
    
  CompilerEndIf

Bernd

Posted: **Wed Dec 27, 2017 7:47 am**

That works great, thank you very much !!!

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