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“4137X˙CH04˙Akerkar” — 2007/9/17 — 11:02 — page 169 — #51
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4.4 Association 169
In the candidate-generation step,
• from {2, 3} and {2, 4}, we get {2, 3, 4}
• from {3, 5} and {3, 7}, we get {3, 5, 7}, and likewise
• from {5, 6} and {5, 7}, we get {5, 6, 7}.
C
3
:= {{2, 3, 4}, {3, 5, 7}, {5, 6, 7}}.
The pruning step prunes {2, 3, 4} as not all its subsets of size 2; that is, {2, 3}, {2, 4},
{3, 4} are present in L
2
.
The other two itemsets are reserved.
Thus, the pruned C
3
is {{3, 5, 7}, {5, 6, 7}}.
Read the database to count the support of the itemsets in C
3
to get
L
3
:= {{3, 5, 7}→3}.
k := 4
Because L
3
contains only one element, C
4
is empty and the algorithm ...