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I am trying to do some market basket analysis using the arules package, but when I use the summary() function on an itemMatrix object to check which are the most frequent items, the numbers do not add up. If I do:

library(arules)
x <- read.transactions("Supermarket2014-15.csv")
summary(x)

I get:

transactions as itemMatrix in sparse format with
 5001 rows (elements/itemsets/transactions) and
 997 columns (items) and a density of 0.003557162 

most frequent items:    
45      28      42      35      22 (Other) 
503     462     444     440     413   15474

But if I check with a for loop, or even in Excel, the count for the product 45 is 513 and not 503. The same for 28, which should be 499, and so on. The odd thing is if I sum up all the totals (15474+413+440+444+462+503) I get the correct number for the total of transacted products.

The data has several NA values and products are factors.

str(x)

And here is the raw data (Day ranges from 1 to 28, Product ranges from 1 to 50):

Raw Data

Ben Bolker
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JoaoBrito
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    actually, I'm not sure. Is there any chance we can have a reproducible example? – Ben Bolker Dec 26 '16 at 18:42
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    ... and are there any `NA` values in your data set? – Ben Bolker Dec 26 '16 at 18:44
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    I also wonder if the products are numbers or a factor. If a factor, do you have "45" and "45 " with a blank? – G5W Dec 26 '16 at 18:45
  • try `str(x)` and show as the result please – Derek Corcoran Dec 26 '16 at 18:47
  • Welcome to Stack Overflow! This is still not reproducible (and please don't post screenshots -- cut and paste text instead) -- please read [mcve] and [this set of r-specific advice](http://stackoverflow.com/questions/5963269/how-to-make-a-great-r-reproducible-example) ... – Ben Bolker Dec 26 '16 at 21:04

1 Answers1

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If you look at the result of your str(x) call then you see under @iteminfo and $labels that some items have labels like "1;1", etc. This means that the items are not correctly separated after reading the file in. The default separator in read.transactions() is a white space, but you seem to have (some) semicolons there. Try sep=";" in read.transactions().

Michael Hahsler
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