Note that you can't have a *
in column names (see ?make.names
). Here is a basic approach:
Split
Year_store
into two separate columnsYear
andStore
in your data frame; at the moment it contains two completely different kinds of data and you actually need to process them separately.Make a
NextYear
column, defined asYear + 1
Make a
NextStore
column, in which you assign the store code matchingCustomer_Id
and for whichYear
is the same as this row'sNextYear
, assigningNA
if there is no record of the customer visiting a store the next year, and throwing an error if the data do not meet the required specification (are ambiguous about which store was visited first the next year).Strip out any of the rows in which
NextStore
isNA
, and combine theNextYear
andNextStore
columns into aNextYear_NextStore
column.Summarize your data frame by the
Year_store
andNextYear_NextStore
columns e.g. usingddply
in theplyr
package.
Some sample data:
# same example data as question
customer.df <- data.frame(Customer_Id = c(1, 1, 1, 2, 2, 2),
Year_Store = c("2010_A", "2011_B", "2012_C", "2010_A", "2011_B", "2012_D"),
stringsAsFactors = FALSE)
# alternative data should throw error, customer 2 is inconsistent in 2011
badCustomer.df <- data.frame(Customer_Id = c(1, 1, 1, 2, 2, 2),
Year_Store = c("2010_A", "2011_B", "2012_C", "2010_A", "2011_B", "2011_D"),
stringsAsFactors = FALSE)
And an implementation:
require(plyr)
splitYearStore <- function(df) {
df$Year <- as.numeric(substring(df$Year_Store, 1, 4))
df$Store <- as.character(substring(df$Year_Store, 6))
return(df)
}
findNextStore <- function(df, matchCust, matchYear) {
matchingStore <- with(df,
df[Customer_Id == matchCust & Year == matchYear, "Store"])
if (length(matchingStore) == 0) {
return(NA)
} else if (length(matchingStore) > 1) {
errorString <- paste("Inconsistent store results for customer",
matchCust, "in year", matchYear)
stop(errorString)
} else {
return(matchingStore)
}
}
tabulateTransitions <- function(df) {
df <- splitYearStore(df)
df$NextYear <- df$Year + 1
df$NextStore <- mapply(findNextStore, matchCust = df$Customer_Id,
matchYear = df$NextYear, MoreArgs = list(df = df))
df$NextYear_NextStore <- with(df, paste(NextYear, NextStore, sep = "_"))
df <- df[!is.na(df$NextStore),]
df <- ddply(df, .(Source = Year_Store, Target = NextYear_NextStore),
summarise, No_Customers = length(Customer_Id))
return(df)
}
Results:
> tabulateTransitions(customer.df)
Source Target No_Customers
1 2010_A 2011_B 2
2 2011_B 2012_C 1
3 2011_B 2012_D 1
> tabulateTransitions(badCustomer.df)
Error in function (df, matchCust, matchYear) :
Inconsistent store results for customer 2 in year 2011
No attempt has been made to optimise; if your data set is massive then perhaps you should investigate a data.table
solution.