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From Apache Wiki <wikidi...@apache.org>
Subject [Solr Wiki] Update of "FunctionQuery" by HossMan
Date Fri, 10 Jul 2009 00:15:16 GMT
Dear Wiki user,

You have subscribed to a wiki page or wiki category on "Solr Wiki" for change notification.

The following page has been changed by HossMan:
http://wiki.apache.org/solr/FunctionQuery

The comment on the change is:
normalize headers and indenting 

------------------------------------------------------------------------------
   1. Embed a FunctionQuery in a regular query expressed in SolrQuerySyntax via the _val_
hook
   1. Use the FunctionQ!ParserPlugin, ie: {{{q={!func}log(foo)}}}
   1. Use a parameter that has an explicit type of FunctionQuery, such as DisMaxRequestHandler's
'''bf''' (boost function) parameter.
-      NOTE: the '''bf''' parameter actually takes a list of function queries separated by
whitespace and each with an optional boost.  Make sure to eliminate any internal whitespace
in single function queries when using '''bf'''.
+     * NOTE: the '''bf''' parameter actually takes a list of function queries separated by
whitespace and each with an optional boost.  Make sure to eliminate any internal whitespace
in single function queries when using '''bf'''.
-      Example: {{{q=dismax&bf="ord(popularity)^0.5 recip(rord(price),1,1000,1000)^0.3"}}}
+     * Example: {{{q=dismax&bf="ord(popularity)^0.5 recip(rord(price),1,1000,1000)^0.3"}}}
  
  = Function Query Syntax =
  There is currently no infix parser - functions must be expressed as function calls (e.g.
sum(a,b) instead of a+b)
  
  = Available Functions =
  
- === constant ===
+ == constant ==
  <!> ["Solr1.3"]
  Floating point constants.
      Example Syntax: '''1.5'''
  
      SolrQuerySyntax Example: '''_val_:1.5'''
  
- === fieldvalue ===
+ == fieldvalue ==
  This function returns the numeric field value of an indexed field with a maximum of one
value per document (not multiValued).  The syntax is simply the field name by itself.  0 is
returned for documents without a value in the field.
      Example Syntax: '''myFloatField'''
  
      SolrQuerySyntax Example: '''_val_:myFloatField'''
  
- === ord ===
+ == ord ==
  ord(myfield) returns the ordinal of the indexed field value within the indexed list of terms
for that field in lucene index order (lexicographically ordered by unicode value), starting
at 1. In other words, for a given field, all values are ordered lexicographically; this function
then returns the offset of a particular value in that ordering. The field must have a maximum
of one value per document (not multiValued).  0 is returned for documents without a value
in the field.
     Example: If there were only three values for a particular field: "apple","banana","pear",
then ord("apple")=1, ord("banana")=2, ord("pear")=3 
  
@@ -40, +40 @@

  
  WARNING: ord() depends on the position in an index and can thus change when other documents
are inserted or deleted, or if a !MultiSearcher is used.
  
- === rord ===
+ == rord ==
  The reverse ordering of what ord provides.
      Example Syntax: '''rord(myIndexedField)'''
  
      Example: '''rord(myDateField)''' is a metric for how old a document is: the youngest
document will return 1, the oldest document will return the total number of documents.
  
- === sum ===
+ == sum ==
  <!> ["Solr1.3"]
  sum(x,y,...) returns the sum of multiple functions.
      Example Syntax: '''sum(x,1)'''
@@ -55, +55 @@

  
      Example Syntax: '''sum(sqrt(x),log(y),z,0.5)'''
  
- === product ===
+ == product ==
  <!> ["Solr1.3"]
  product(x,y,...) returns the product of multiple functions.
      Example Syntax: '''product(x,2)'''
  
      Example Syntax: '''product(x,y)'''
  
- === div ===
+ == div ==
  <!> ["Solr1.3"]
  div(x,y) divides the function x by the function y.
      Example Syntax: '''div(1,x)'''
  
      Example Syntax: '''div(sum(x,100),max(y,1))'''
  
- === pow ===
+ == pow ==
  <!> ["Solr1.3"]
  pow(x,y) raises the base x to the power y.
      Example Syntax: '''pow(x,0.5)'''   same as sqrt
  
      Example Syntax: '''pow(x,log(y))'''
  
- === abs ===
+ == abs ==
  <!> ["Solr1.3"]
  abs(x) returns the absolute value of a function.
      Example Syntax: '''abs(-5)'''
  
      Example Syntax: '''abs(x)'''
  
- === log ===
+ == log ==
  <!> ["Solr1.3"]
  log(x) returns log base 10 of the function x.
      Example Syntax: '''log(x)'''
  
      Example Syntax: '''log(sum(x,100))'''
  
- === sqrt ===
+ == sqrt ==
  <!> ["Solr1.3"]
  sqrt(x) returns the square root of the function x
      Example Syntax: '''sqrt(2)'''
  
      Example Syntax: '''sqrt(sum(x,100))'''
  
- === map ===
+ == map ==
  <!> ["Solr1.3"]
  map(x,min,max,target) maps any values of the function x that fall within min and max inclusive
to target.  min,max,target are constants. It outputs the field's value if it does not fall
between min and max.
      Example Syntax 1: '''map(x,0,0,1)'''  change any values of 0 to 1... useful in handling
default 0 values
@@ -107, +107 @@

  
  
  
- === scale ===
+ == scale ==
  <!> ["Solr1.3"]
  scale(x,minTarget,maxTarget) scales values of the function x such that they fall between
minTarget and maxTarget inclusive.
      Example Syntax: '''scale(x,1,2)'''  all values will be between 1 and 2 inclusive.
@@ -116, +116 @@

  
      NOTE: This implementation currently cannot distinguish when documents have been deleted
or documents that have no value, and 0.0 values will be used for these cases.  This means
that if values are normally all greater than 0.0, one can still end up with 0.0 as the min
value to map from.  In these cases, an appropriate map() function could be used as a workaround
to change 0.0 to a value in the real range.  example: '''scale(map(x,0,0,5),1,2)'''
  
- === query ===
+ == query ==
  <!> ["Solr1.4"]
  query(subquery, default) returns the score for the given subquery, or the default value
for documents not matching the query.  Any type of subquery is supported through either parameter
dereferencing {{{$otherparam}}} or direct specification of the query string in the LocalParams
via "v".
  
@@ -128, +128 @@

  
      Example Syntax: '''q=product(popularity, query($qq,0.1)&qq={!dismax}solr rocks'''
specifies a default score of 0.1 for documents that don't match the dismax query.
  
- === linear ===
+ == linear ==
  linear(x,m,c) implements m*x+c where m and c are constants and x is an arbitrary function.
 This is equivalent to '''sum(product(m,x),c)''', but slightly more efficient as it is implemented
as a single function.
      Example Syntax: '''linear(x,2,4)'''  returns 2*x+4
  
- === recip ===
+ == recip ==
  A reciprocal function with '''recip(myfield,m,a,b)''' implementing a/(m*x+b).  m,a,b are
constants, x is any arbitrarily complex function.
  
  When a and b are equal, and x>=0, this function has a maximum value of 1 that drops as
x increases. Increasing the value of a and b together results in a movement of the entire
function to a flatter part of the curve. These properties can make this an ideal function
for boosting more recent documents when x is rord(datefield).
      Example Syntax: '''recip(rord(creationDate),1,1000,1000)'''
  
- === max ===
+ == max ==
  max(x,c) returns the max of another function and a constant.  Useful for "bottoming out"
another function at some constant.
      Example Syntax: '''max(myfield,0)'''
  
- === top ===
+ == top ==
  <!> ["Solr1.4"]
  Causes it's function query argument to derive it's values from the top-level IndexReader
containing all parts of an index.  For example, the ordinal of a value in a single segment
will be different from the ordinal of that same value in the complete index.  The ord() and
rord() functions implicitly use top() and hence ord(foo) is equivalent to top(ord(foo)).
  
- === General Example ===
+ = General Example =
-     To give more idea about the use of the function query, suppose index stores dimensions
in meters '''x''', '''y''','''z''' of some hypothetical boxes with arbitrary names stored
in field '''boxname'''.
-     Suppose we want to search for box matching name ''findbox'' but ranked according to
volumes of boxes, the query params would be:
  
+ To give more idea about the use of the function query, suppose index stores dimensions in
meters '''x''', '''y''','''z''' of some hypothetical boxes with arbitrary names stored in
field '''boxname'''.
+ Suppose we want to search for box matching name ''findbox'' but ranked according to volumes
of boxes, the query params would be:
+ {{{
-      '''q=boxname:findbox _val_:"product(product(x,y),z)"'''.
+   q=boxname:findbox+_val_:"product(product(x,y),z)"
+ }}}
  
-     Although this will rank the results based on volumes but in order to get the computed
volume you will need to add parameter:
+ Although this will rank the results based on volumes but in order to get the computed volume
you will need to add parameter...
+ {{{
+   &fl=*,score
+ }}}
  
-     '''&fl=*, score'''   where '''score''' will contain the resultant volume.
+ ...where '''score''' will contain the resultant volume.
  
+ Suppose you also have a field containing weight of the box as 'weight', then to sort by
the density of the box and return the value of the density in score you query should be...
  
+ {{{
-     Suppose you also have a field containing weight of the box as 'weight', then to sort
by the density of the box and return the value of the density in score you query should be:
- 
- 
-     '''http ://localhost:8983/solr/select/?q=boxname:findbox _val_:"div(weight,product(product(x,y),z))"&fl=boxname
x y z weight score'''
+ http://localhost:8983/solr/select/?q=boxname:findbox+_val_:"div(weight,product(product(x,y),z))"&fl=boxname,x,y,z,weight,score
+ }}}
      
  

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