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From Chris Hostetter <>
Subject Re: faceting and categorizing on color?
Date Mon, 19 Jun 2006 08:12:11 GMT

: I have been reading several threads about facet counts
: and category counts and was wondering if/how they
: might apply to searching for colors. Let's say that

First off, let me clear up somethign regarding your index field structure,
you mentioned that you currently have documents that look like this...

: E00000 EE0000 EEE000 EEEE00


: If I setup the COLORS field such that it is of type
: Field.Keyword, then I can construct a query
: COLORS:FFFFFF with a StandardAnalyzer that returns the

If you are indexing it as Field.Keyword and you can query for
COLORS:FFFFFF and get results, then either you are only only getting
documents that are 100% white, or when you indexed the Documents you added
eeach collor as a seperate field instance -- I'm going to assume it's the
later, which makes perfect sense and is a reasonable way to do things, but
it's also exactly the same as what you ask about a little later..

: Am I mistaken in thinking that my problem is similar
: to faceting/categorization/rollup, just on a different
: scale? I suppose I could also structure my document
: such that it looked like this:
: Field Value
: COLOR F00000
: COLOR FF0000

...unless of course, i'm completley missunderstanding you.

On to the meat of your question...

: performance hit.This thread from last year:
: Seems to suggest the creation of a String[] of colors
: and then iterate over it using a QueryFilter, AND'ing
: the result sets bits with the filtered bits, sorting
: based on cardinality. That works in my tests with a
: limited number of colors, but my String[] of colors
: could contain 16.7M values, and most certainly will
: contain at least several million.

Actually, the idea behind that approach is that you *want* to build up a
QueryFilter (or some other BitSetish thing) for every possible term value,
even if most of the time you won't be looking at all of them
because you can reuse a differnet subset of all of them on every query --
it's a time/space tradeoff, really fast set lookups/intersections in
exchange of a lot of RAM.

: Am I mistaken in thinking that my problem is similar
: to faceting/categorization/rollup, just on a different

You're not mistaken.  One thing you may want to consider is wether or not
it's really usefull to provide "facet" counts for each of the unique
color values in the 256^3 RGB spectrum, or if it's better (and easier) to
facet on the most significant bytes of the color value.  Searching for
"white" and seeing...

     FFFFFF  22,143 photos
     FFFFFE  22,134 photos
     FEFFFF  22,121 photos
     FFFEFF  22,098 photos
     FEFFFE  22,088 photos the top 5 common colors in my results isn't all the helpfull is it?

If you index both the full color codes as well as just the most
significant hex characters from the RGB code in seperate fields, you can
do "coarse" faceting on one field, and "refined" faceting on the other...

COLOR: FFFFFE FFA3B4 2287C3 773442 666BED

: That would allow me to do something with TermEnums,
: but I don't see how it would be any better than using
: a HitCollector. Does the above document structure make

Usually, you need to do one pass over your values and one pass over
your documents -- with a HitCollector you do a pass over your values first
(either by constructing a FieldCache or by doing something fancy with
TermEnum).  Alternately, you can do one pass over your documents building
a BitSet of the docs that match, and *then* do a pass over the values
using a TermEnum/TermDocs to get interestign stats about them

If you are interested in doing the coarse appraoch, the QueryFilter/BitSet
approach would probably work very well (only 4096 total BitSets ever).
Once a coarse color was choosen you can use the TermEnum to get a list of
all the subtle shades and TermDocs to check which docs already in your set
match on that shade.

if you store the least significant hex characters last, you can reduce
the amount of skipping arround you have to do...

COLOR: FFFFFE FFA3B4 2587C3 773442 666BED

: initial document structure? If the answer to my
: question is trivial would anything change if I wanted
: to weight the colors. For example, if the initial
: document looked like:
: Field	Value
: COLORS	10-F00000 6-FF0000 3-FFF000 9-FFFF00 7-FFFFF0
: 1-FFFFFF 2-E00000 4-EE0000 8-EEE000 5-EEEE00
: PIXELS	10000
: That would be interpreted as FFFFFF is the most
: dominant of the top 10 most dominant colors and F00000
: is the least. Would that be a terrible document
: structure?

thigns certainly get a lot harder when you want to weight them ... but not
impossible.  Using term frequencies would probably be the best way to do
this (ie: add COLORS:F00000 to the 10 times, and COLOR:FFFFFF only once)
and would have the added benefit that this document would score better on
a search for COLORS:F00000 then it would on a search for COLOR:FFFFFF.


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