An Approach of Improvisation in Efficiency of Apriori Algorithm

ISSN: 2312-7694
Sakshi et al, / International Journal of Computer and Communication System Engineering (IJCCSE), Vol. 2 (5), 2015, 659-664
659 | P a g e
© IJCCSE All Rights Reserved Vol. 02 No.05 Oct 2015 www.ijccse.com
An Approach of Improvisation in Efficiency of
Apriori Algorithm
Sakshi Aggarwal
SGT Institute of Engineering & Technology
Gurgaon, Haryana
sakshii.26@gmail.com
Dr. Ritu Sindhu
SGT Institute of Engineering & Technology
Gurgaon, Haryana
ritu.sindhu2628@gmail.com
Abstract— Association rule mining is used to find frequent
itemsets in data mining. Classical apriori algorithm is inefficient
due to large scans of the transaction database to find frequent
item sets. In this paper, we are proposing a method to improve
Apriori algorithm efficiency by reducing the database size as well
as reducing the time wasted on scanning the transactions.
Index Terms— Apriori algorithm, Support, Frequent Itemset,
Association rules, Candidate Item
I. INTRODUCTION
Extracting relevant information by exploitation of data is
called Data Mining. There is an increasing need to extract valid
and useful information by business people from large datasets
[2]; here data mining achieves its goal. Thus, data mining has
its importance to discover hidden patterns from huge data
stored in databases, OLAP (Online Analytical Process), data
warehouse etc. [5]. This is the only reason why data mining is
also known as KDD (Knowledge Discovery in Databases). [4]
KDD’s techniques are used to extract the interesting patterns.
Steps of KDD process are cleaning of data (data cleaning),
selecting relevant data, transformation of data, data pre-
processing, mining and pattern evaluation.
II. ASSOCIATION RULE MINING
Association rule mining has its importance in fields of
artificial intelligence, information science, database and many
others. Data volumes are dramatically increasing by day-to-day
activities. Therefore, mining the association rules from massive
data is in the interest for many industries as theses rules help in
decision-making processes, market basket analysis and cross
marketing etc.
Association rule problems are in discussion from 1993 and
many researchers have worked on it to optimize the original
algorithm such as doing random sampling, declining rules,
changing storing framework etc. [1]. We find association rules
from a huge amount of data to identify the relationships in
items which tells about human behavior of buying set of items.
There is always a particular pattern followed by humans during
buying the set of items.
In data mining, unknown dependency in data is found in
association rule mining and then rules between the items are
found [3]. Association rule mining problem is defined as
follows.
DBT = {T1, T2,...,TN } is a database of N T transactions.
Each transaction consists of I, where I= {i1, i2, i3….iN} is a
set of all items. An association rule is of the form A⇒B, where
A and B are item sets, A⊆I, B⊆I, A∩B=∅. The whole point of
an algorithm is to extract the useful information from these
transactions.
For example: Consider below table containing some
transactions:
TABLE I. EXAMPLE OF TRANSACTIONS IN A DATABASE
TID Items
1 CPU, Monitor
2 CPU, Keyboard, Mouse, UPS
3 Monitor, Keyboard, Mouse, Motherboard
4
CPU, Monitor, Keyboard, Mouse
5 CPU, Monitor, Keyboard, Motherboard
Example of Association Rules:
{Keyboard}  {Mouse},
{CPU, Monitor}  {UPS, Motherboard},
{CPU, Mouse}  {Monitor},
A B is an association rule (A and B are itemsets).
Example: {Monitor, Keyboard}  {Mouse}
Rule Evaluation:
Support: It is defined as rate of occurrence of an itemset in
a transaction database.
Support (Keyboard  Mouse) =
No. Of transactions containing both Keyboard and Mouse
No. Of total transactions
Confidence: For all transactions, it defines the ratio of data
items which contains Y in the items that contains X.

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Confidence (Keyboard  Mouse) =
No. Of transactions containing Keyboard and Mouse
No. Of transactions (containing Keyboard)
Itemset: One or more items collectively are called an
itemset.
Example {Monitor, Keyboard, Mouse}. K-itemset
contains k-items.
Frequent Itemset: For a frequent item set:
SI >= min_sup
Where I is an itemset, min_sup is minimum support
threshold and S represent the support for an itemset.
III. CLASSICAL APRIORI ALGORITHM
Using an iterative approach, in each iteration Apriori
algorithm generates candidate item-sets by using large itemsets
of a previous iteration. [2]. Basic concept of this iterative
approach is as follows:
Algorithm Apriori_algo(Lk)
1. L1= {frequent-1 item-sets};
2. for (k=2; Lk-1≠Φ; k++) {
3. Ck= generate_Apriori(Lk-1); //New candidates
4. forall transactions t ϵ D do begin
5. Ct=subset(Ck,t); //Candidates contained in t
6. forall candidates c ϵ Ct do
7. c.count++;
8. }
9. Lk={c ϵ Ck | c.count≥minsup}
10. end for
11. Answer=UkLk
Algorithm 1: Apriori Algorithm [6]
Above algorithm is the apriori algorithm. In above,
database is scanned to find frequent 1-itemsets along with the
count of each item. Frequent itemset L1 is created from
candidate item set where each item satisfies minimum support.
In next each iteration, set of item sets is used as a seed which
is used to generate next set of large itemsets i.e candidate item
sets (candidate generation) using apriori_gen function.
Lk-1 is input to generate_Apriori function and returns Ck.
Join step joins Lk-1 with another Lk-1 and in prune step, item
sets
c ϵ Ck are deleted such that (k-1) is the subset of “c” but not
in Lk-1 of Ck-1.
Algorithm generate_Apriori (Lk)
1. insert into Ck
2. p=Lk-1 ,q= Lk-1
3. select p.I1,p.I2,.....p.Ik-1,q.Ik-1 from p,q
where p.I1=q.I1.....p.Ik-2= q.Ik-2,p.Ik-1<q.Ik-1;
4. forall itemsets c ϵ Ck do
5. forall { s ⊃ (k-1) of c) do
6. if(s ∉ Lk-1) then
7. from Ck , delete c
Algorithm 2: Apriori-Gen Function[6]
Fig 1: Apriori Algoithm Steps
A. Limitations of Apriori Algorithm
 Large number of candidate and frequent item sets are
to be handled and results in increased cost and waste of
time.
Example: if number of frequent (k-1) items is 104
then
almost 107
Ck need to be generated and tested [2]. So
scanning of a database is done many times to find Ck.
 Apriori is inefficient in terms of memory requirement
when large numbers of transactions are in
consideration.

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IV. PROPOSED ENHANCEMENT IN EXISTING APRIORI
ALGORITHM
Below section will give an idea to improve apriori
efficiency along with example and algorithm.
A. Improvement of Apriori
In this approach to improve apriori algorithm efficiency, we
focus on reducing the time consumed for Ck generation.
In the process to find frequent item sets, first size of a
transaction (ST) is found for each transaction in DB and
maintained. Now, find L1 containing set of items, support
value for each item and transaction ids containing the item.
Use L1 to generate L2, L3… along with decreasing the
database size so that time reduces to scan the transaction from
the database.
To generate C2(x,y) (items in Ck are x and y), do L(k-1) * L(k-
1) . To find L2 from C2, instead of scanning complete database
and all transactions, we remove transaction where ST < k
(where k is 2, 3…) and also remove the deleted transaction
from L1 as well. This helps in reducing the time to scan the
infrequent transactions from the database.
Find minimum support from x and y and get transaction ids
of minimum support count item from L1. Now, Ck is scanned
for specific transactions only (obtained above) and from
decreased DB size. Then, L2 is generated by C2 where support
of Ck >= min_supp.
C3(x,y,z), L3 and so on is generated repeating above steps
until no frequent items sets can be discovered.
Algorithm Apriori
Input: transactions database, D
Minimum support, min_sup
Output Lk: frequent itemsets in D
1. Find ST //for each transaction in DB
2. L1= find frequent_1_itemset (D)
3. L1+=get_txn_ids(D)
4. for (k=2;Lk-1≠Φ ; k++){
5. Ck=generate_candidate(Lk-1)
6. x= item_min_sup(Ck, L1) //find item from Ck(a,b)
which has minimum support using L1
7. target=get_txn_ids(x) //get transactions for each item
8. for each(txn t in tgt) do{
9. Ck.count++
10. Lk= (items in Ck>=min_sup)
11. } //end foreach
12. foreach(txn in D){
13. if (ST=(k-1))
14. txn_set+=txn
15. } //end foreach
16. delete_txn_DB(txn_set) //reduce DB size
17. delete_txn_L1(txn_set,L1) //reduce transaction size in
L1
18. } //end for
Fig 2: Proposed Apriori Algoithm Steps

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V. EXPERIMENTAL EXAMPLE
Below is the transaction database (D) having 10
transactions and min_sup=3. Size of transaction (ST) is
calculated for each transaction. (Refer Fig. 3).
Fig 3: Transaction Database
All the transactions are scanned to get frequent-1-itemset,
L1. It contains items, respective support count and transactions
from D which contain the items. Infrequent candidates’ i.e.
itemsets whose support < min_sup are eliminated or deleted.
(Refer Fig. 4 and Fig. 5)
Fig 4: Candidate-1-itemset
Fig 5: Frequent-1-itemset
From L1, frequent-2-itemset (L2) is generated as follows.
Example: consider itemset {I1, I2}. In classical apriori, all
transactions are scanned to find {I1, I2} in D. But in our
proposed idea, firstly, transaction T9 is deleted from D as well
as from L1 as ST for T9 is less than k (k=2). New D and L1 are
shown in Fig. 6 and Fig. 7 respectively. Secondly, {I1, I2} is
split into {I1} and {I2} and item with minimum support i.e.
{I1} is selected using L1 and its transactions will be used in L2.
So, {I1, I2} will be searched only in transactions which contain
{I1} i.e. T1, T3, T7, T10.
So, searching time is reduced twice:
 by reducing database size
 By cutting down the number of transactions to be
scanned.
L2 is shown in Fig. 8.
Fig 6: Transaction Database (updated)

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Fig 7: Frequent-1-itemset (updated)
To generate frequent-3-itemset (L3), D is updated by
deleting transactions T6 andT10 as ST for these transactions is
less than k (k=3). L1 is also updated by deleting transactions
T6 and T10. Then, repeating above process, L3 is generated and
infrequent itemsets are deleted. Refer Fig. 9, Fig. 10 and Fig.
11 for updated database, L1 and L3 respectively.
Fig 9: Transaction Database (updated)
Fig 10: Frequent-1-itemset (updated)
So, above process is followed to find frequent-k-itemset for
a given transaction database. Using frequent-k-itemset,
association rules are generated from non-empty subsets which
satisfy minimum confidence value.
VI. COMPARATIVE ANALYSIS
We have counted the number of transactions that are
scanned to find L1, L2 and L3 for our given example and below
table shows the difference in count of transactions scanned by
using original apriori algorithm and our proposed idea.
Fig 12: Comparative Results
For k=1, number of transactions scanned is same for both
classical apriori and our proposed idea but with the increase in
k, count of transactions decrease. Refer Fig. 13.

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Fig 13: Comparative Analysis
VII. CONCLUSION
We have proposed an idea to improve the efficiency of
apriori algorithm by reducing the time taken to scan database
transactions. We find that with increase in value of k, number
of transactions scanned decreases and thus, time consumed
also decreases in comparison to classical apriori algorithm.
Because of this, time taken to generate candidate item sets
in our idea also decreases in comparison to classical apriori.
REFERENCES
[1] J. Han and M. Kamber, Conception and Technology of Data
Mining, Beijing: China Machine Press, 2007.
[2] U. Fayyad, G. Piatetsky-Shapiro, and P. Smyth, “From data
mining to knowledge discovery in databases,” vol. 17, no. 3, AI
magazine, 1996, pp. 37.
[3] S. Rao, R. Gupta, “Implementing Improved Algorithm over
APRIORI Data Mining Association Rule Algorithm”,
International Journal of Computer Science And Technology, pp.
489-493, Mar. 2012
[4] H. H. O. Nasereddin, “Stream data mining,” International
Journal of Web Applications, vol. 1, no. 4,pp. 183–190, 2009.
[5] M. Halkidi, “Quality assessment and uncertainty handling in
data mining process,” in Proc, EDBT Conference, Konstanz,
Germany, 2000.
[6] Rakesh Agarwal, Ramakrishna Srikant, “Fast Algorithm for
mining association rules” VLDB Conference Santiago, Chile,
1994, pp 487-499.

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