library(arules)
## Loading required package: Matrix
## 
## Attaching package: 'arules'
## The following objects are masked from 'package:base':
## 
##     abbreviate, write
data(Groceries) 
set.seed(1)
head(Groceries)
## transactions in sparse format with
##  6 transactions (rows) and
##  169 items (columns)
groc<- as(Groceries,"transactions")
groc
## transactions in sparse format with
##  9835 transactions (rows) and
##  169 items (columns)
summary(groc)
## transactions as itemMatrix in sparse format with
##  9835 rows (elements/itemsets/transactions) and
##  169 columns (items) and a density of 0.02609146 
## 
## most frequent items:
##       whole milk other vegetables       rolls/buns             soda 
##             2513             1903             1809             1715 
##           yogurt          (Other) 
##             1372            34055 
## 
## element (itemset/transaction) length distribution:
## sizes
##    1    2    3    4    5    6    7    8    9   10   11   12   13   14   15 
## 2159 1643 1299 1005  855  645  545  438  350  246  182  117   78   77   55 
##   16   17   18   19   20   21   22   23   24   26   27   28   29   32 
##   46   29   14   14    9   11    4    6    1    1    1    1    3    1 
## 
##    Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
##   1.000   2.000   3.000   4.409   6.000  32.000 
## 
## includes extended item information - examples:
##        labels  level2           level1
## 1 frankfurter sausage meat and sausage
## 2     sausage sausage meat and sausage
## 3  liver loaf sausage meat and sausage
itemFrequencyPlot(groc,support=.06,cex.names=1.5)

The item frequency plot is there to show the most frequently bought items.

grocerules <- apriori(groc,parameter=list(support=0.01,confidence=0.5))
## Apriori
## 
## Parameter specification:
##  confidence minval smax arem  aval originalSupport maxtime support minlen
##         0.5    0.1    1 none FALSE            TRUE       5    0.01      1
##  maxlen target   ext
##      10  rules FALSE
## 
## Algorithmic control:
##  filter tree heap memopt load sort verbose
##     0.1 TRUE TRUE  FALSE TRUE    2    TRUE
## 
## Absolute minimum support count: 98 
## 
## set item appearances ...[0 item(s)] done [0.00s].
## set transactions ...[169 item(s), 9835 transaction(s)] done [0.00s].
## sorting and recoding items ... [88 item(s)] done [0.00s].
## creating transaction tree ... done [0.00s].
## checking subsets of size 1 2 3 4 done [0.00s].
## writing ... [15 rule(s)] done [0.00s].
## creating S4 object  ... done [0.00s].
inspect(grocerules)
##      lhs                     rhs                   support confidence     lift count
## [1]  {curd,                                                                         
##       yogurt}             => {whole milk}       0.01006609  0.5823529 2.279125    99
## [2]  {other vegetables,                                                             
##       butter}             => {whole milk}       0.01148958  0.5736041 2.244885   113
## [3]  {other vegetables,                                                             
##       domestic eggs}      => {whole milk}       0.01230300  0.5525114 2.162336   121
## [4]  {yogurt,                                                                       
##       whipped/sour cream} => {whole milk}       0.01087951  0.5245098 2.052747   107
## [5]  {other vegetables,                                                             
##       whipped/sour cream} => {whole milk}       0.01464159  0.5070423 1.984385   144
## [6]  {pip fruit,                                                                    
##       other vegetables}   => {whole milk}       0.01352313  0.5175097 2.025351   133
## [7]  {citrus fruit,                                                                 
##       root vegetables}    => {other vegetables} 0.01037112  0.5862069 3.029608   102
## [8]  {tropical fruit,                                                               
##       root vegetables}    => {other vegetables} 0.01230300  0.5845411 3.020999   121
## [9]  {tropical fruit,                                                               
##       root vegetables}    => {whole milk}       0.01199797  0.5700483 2.230969   118
## [10] {tropical fruit,                                                               
##       yogurt}             => {whole milk}       0.01514997  0.5173611 2.024770   149
## [11] {root vegetables,                                                              
##       yogurt}             => {other vegetables} 0.01291307  0.5000000 2.584078   127
## [12] {root vegetables,                                                              
##       yogurt}             => {whole milk}       0.01453991  0.5629921 2.203354   143
## [13] {root vegetables,                                                              
##       rolls/buns}         => {other vegetables} 0.01220132  0.5020921 2.594890   120
## [14] {root vegetables,                                                              
##       rolls/buns}         => {whole milk}       0.01270971  0.5230126 2.046888   125
## [15] {other vegetables,                                                             
##       yogurt}             => {whole milk}       0.02226741  0.5128806 2.007235   219
inspect(sort(subset(grocerules, subset=lift > 2.25), by="support"))
##     lhs                  rhs                   support confidence     lift count
## [1] {root vegetables,                                                           
##      yogurt}          => {other vegetables} 0.01291307  0.5000000 2.584078   127
## [2] {tropical fruit,                                                            
##      root vegetables} => {other vegetables} 0.01230300  0.5845411 3.020999   121
## [3] {root vegetables,                                                           
##      rolls/buns}      => {other vegetables} 0.01220132  0.5020921 2.594890   120
## [4] {citrus fruit,                                                              
##      root vegetables} => {other vegetables} 0.01037112  0.5862069 3.029608   102
## [5] {curd,                                                                      
##      yogurt}          => {whole milk}       0.01006609  0.5823529 2.279125    99

All the rules have fairly small support, confidence and lifts. To pick one, rule 2 is probably the most supported. It has the second best support, second best confidence and second best lift. This is strong considering the rules that come in first for support, confidence and lift, are low in other categories. By looking at all 3, it will give a better representation of all factors and not just focusing on one; for example, only looking at confidence. Rule 2 also has the second highest count, which means 121 cases occured with rule 2.