README.md in bmg-0.19.1 vs README.md in bmg-0.19.2
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+ new
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# Bmg, a relational algebra (Alf's successor)!
-[](https://travis-ci.com/enspirit/bmg)
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Bmg is a relational algebra implemented as a ruby library. It implements the
[Relation as First-Class Citizen](http://www.try-alf.org/blog/2013-10-21-relations-as-first-class-citizen)
paradigm contributed with [Alf](http://www.try-alf.org/) a few years ago.
Bmg can be used to query relations in memory, from various files, SQL databases,
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r.allbut([:a, :b, ...]) # remove specified attributes
r.autowrap(split: '_') # structure a flat relation, split: '_' is the default
r.autosummarize([:a, :b, ...], x: :sum) # (experimental) usual summarizers supported
r.constants(x: 12, ...) # add constant attributes (sometimes useful in unions)
r.extend(x: ->(t){ ... }, ...) # add computed attributes
+r.extend(x: :y) # shortcut for r.extend(x: ->(t){ t[:y] })
r.exclude(predicate) # shortcut for restrict(!predicate)
r.group([:a, :b, ...], :x) # relation-valued attribute from attributes
r.image(right, :x, [:a, :b, ...]) # relation-valued attribute from another relation
r.images({:x => r1, :y => r2}, [:a, ...]) # shortcut over image(r1, :x, ...).image(r2, :y, ...)
r.join(right, [:a, :b, ...]) # natural join on a join key