Optimization for rearrangements

git-svn-id: http://galileo.dmi.unict.it/svn/relational/trunk@145 014f5005-505e-4b48-8d0a-63407b615a7c

complexity

@@ -70,6 +70,14 @@ Notation
    the new tuple was already added to the new relation. And this brings
    the complexity to O(|n|²).
    
+   But the projection can also be used to "rearrange" fields, which
+   makes no sense in pure relational algebra, but can be usefull to make
+   two relations match (in fact it is used internally to make relations
+   match if they have the same fields in different order). In this case
+   there is no need to check if the tuple already exists, because it is
+   assumed that the relation was correct. This gives a complexity of
+   O(|n|) in the best case.
+
 2.  BINARY OPERATORS
 
    Relational defines nine binary operations, and they will be studied
@@ -123,4 +131,5 @@ Notation
 2.9  Join 
 
    Same as above.
+  
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relational/relation.py

@@ -143,7 +143,7 @@ class relation (object):
         Will delete duplicate items
         If an empty list or no parameters are provided, returns None'''    
         #Parameters are supplied in a list, instead with multiple parameters
-        if attributes[0].__class__ == list().__class__:
+        if isinstance(attributes[0],list):
             attributes=attributes[0]
         
         #Avoiding duplicated attributes
@@ -153,6 +153,10 @@ class relation (object):
                 attributes1.append(i)
         attributes=attributes1
         
+        #If source and dest has the same number of attributes, we are just rearranging
+        #so we won't need to check for duplicated entries
+        attributes_same_count=len(attributes)==len(self.header.attributes)
+        
         ids=self.header.getAttributesId(attributes)
         
         if len(ids)==0:
@@ -169,12 +173,10 @@ class relation (object):
             row=[]
             for j in ids:
                 row.append(i[j])
-            if row not in newt.content:#Avoids duplicated items
+                if attributes_same_count or row not in newt.content:
                     newt.content.append(row)
         return newt
     
-        
-    
     def rename(self,params):
         '''Operation rename. Takes a dictionary
         Will replace the itmem with its content.