Data Comparing Algorithms

Here is a general algorithm for comparing two similar tables (or copies of tables).

for r = each record of t1 not in t2 // based on primary key
display record
end-for
for r = each record of t2 not in t1
display record
end-for
for key = each record common to both
r1 = getRecord(t1, key)
r2 = getRecord(t2, key)
for each attribute in r1 not in r2
display key, attribute, and value
end-for
for each attribute in r2 not in r1
display key, attribute, and value
end-for
for attr = each attribute in r1
if r1[attr] not-equal-to r2[attr]
display key, attribute, r1[attr], r2[attr]
end-if
end-for
end-for


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Trees

One technique for comparing trees is to print them as text, and then use text-based difference finders common in most operating systems. Use recursion to create the outline-like format, and perhaps disable white-space sensativity so that different levels won't be over-emphasized. You may want to try it with and without the full node path, as each will emphasize different kinds of changes. Here is a pre-differenced sample text file:

node 1 foo=7 bar=9
..node 1.2 foo=12 bar=7
..node 1.3 foo=9
node 2 bar=6
..node 2.1 foo=12
....node 2.1.1 foo=12 bar=99
..node 2.2 bar=786


(Dots used to prevent TabMunging, but may not otherwise be needed in actual file.)