Compute rolling sum by id variables, with missing timepoints
Here are a few solutions:
1) zoo Using ave, for each group create a monthly series, m, by merging the original series, z, with a grid, g. Then calculate the rolling sum and retain only the original time points:
library(zoo)
f <- function(i) {
z <- with(df[i, ], zoo(count, t))
g <- zoo(, seq(start(z), end(z), by = "month"))
m <- merge(z, g)
window(rollapplyr(m, 4, sum, na.rm = TRUE, partial = TRUE), time(z))
}
df$desired <- ave(1:nrow(df), df$id, df$class, FUN = f)
which gives:
> df
id class t count desired
1 1 A 2010-01-15 1 1
2 1 A 2010-02-15 2 3
3 1 B 2010-04-15 3 3
4 1 B 2010-09-15 4 4
5 2 A 2010-01-15 5 5
6 2 B 2010-06-15 6 6
7 2 B 2010-08-15 7 13
8 2 B 2010-09-15 8 21
Note We have assumed the times are ordered within each group (as in the question). If that is not so then sort df first.
2) sqldf
library(sqldf)
sqldf("select id, class, a.t, a.'count', sum(b.'count') desired
from df a join df b
using(id, class)
where a.t - b.t between 0 and 100
group by id, class, a.t")
which gives:
id class t count desired
1 1 A 2010-01-15 1 1
2 1 A 2010-02-15 2 3
3 1 B 2010-04-15 3 3
4 1 B 2010-09-15 4 4
5 2 A 2010-01-15 5 5
6 2 B 2010-06-15 6 6
7 2 B 2010-08-15 7 13
8 2 B 2010-09-15 8 21
Note: If the merge should be too large to fit into memory then use sqldf("...", dbname = tempfile()) to cause the intermediate results to be stored in a database which it creates on the fly and automatically destroys afterwards.
3) Base R The sqldf solution motivates this base R solution which just translates the SQL into R:
m <- merge(df, df, by = 1:2)
s <- subset(m, t.x - t.y >= 0 & t.x - t.y <= 100)
ag <- aggregate(count.y ~ t.x + class + id, s, sum)
names(ag) <- c("t", "class", "id", "count", "desired")
The result is:
> ag
t class id count desired
1 2010-01-15 A 1 1 1
2 2010-02-15 A 1 2 3
3 2010-04-15 B 1 3 3
4 2010-09-15 B 1 4 4
5 2010-01-15 A 2 5 5
6 2010-06-15 B 2 6 6
7 2010-08-15 B 2 7 13
8 2010-09-15 B 2 8 21
Note: This does do a merge in memory which might be a problem if the data set is very large.
UPDATE: Minor simplifications of first solution and also added second solution.
UPDATE 2: Added third solution.
I'm almost embarrassed to post this. I'm usually pretty good as these, but there's got to be a better way.
This first uses zoo's as.yearmon to get the dates in terms of just month and year, then reshapes it to get one column for each id/class combination, then fills in with zeros before, after, and for missing months, then uses zoo to get the rolling sum, then pulls out just the desired months and merges back with the original data frame.
library(reshape2)
library(zoo)
df$yearmon <- as.yearmon(df$t)
dfa <- dcast(id + class ~ yearmon, data=df, value.var="count")
ida <- dfa[,1:2]
dfa <- t(as.matrix(dfa[,-c(1:2)]))
months <- with(df, seq(min(yearmon)-3/12, max(yearmon)+3/12, by=1/12))
dfb <- array(dim=c(length(months), ncol(dfa)),
dimnames=list(paste(months), colnames(dfa)))
dfb[rownames(dfa),] <- dfa
dfb[is.na(dfb)] <- 0
dfb <- rollsumr(dfb,4, fill=0)
rownames(dfb) <- paste(months)
dfb <- dfb[rownames(dfa),]
dfc <- cbind(ida, t(dfb))
dfc <- melt(dfc, id.vars=c("class", "id"))
names(dfc)[3:4] <- c("yearmon", "desired2")
dfc$yearmon <- as.yearmon(dfc$yearmon)
out <- merge(df,dfc)
> out
id class yearmon t count desired desired2
1 1 A Feb 2010 2010-02-15 2 3 3
2 1 A Jan 2010 2010-01-15 1 1 1
3 1 B Apr 2010 2010-04-15 3 3 3
4 1 B Sep 2010 2010-09-15 4 4 4
5 2 A Jan 2010 2010-01-15 5 5 5
6 2 B Aug 2010 2010-08-15 7 13 13
7 2 B Jun 2010 2010-06-15 6 6 6
8 2 B Sep 2010 2010-09-15 8 21 21
A farily efficient answer to this problem could be found using the data.table library.
##Utilize the data.table package
library("data.table")
data <- data.table(t,class,id,count,desired)[order(id,class)]
##Assign each customer an ID
data[,Cust_No:=.GRP,by=c("id","class")]
##Create "list" of comparison dates and values
Ref <- data[,list(Compare_Value=list(I(count)),Compare_Date=list(I(t))), by=c("id","class")]
##Compare two lists and see of the compare date is within N days
data$Roll.Val <- mapply(FUN = function(RD, NUM) {
d <- as.numeric(Ref$Compare_Date[[NUM]] - RD)
sum((d <= 0 & d >= -124)*Ref$Compare_Value[[NUM]])
}, RD = data$t,NUM=data$Cust_No)
##Print out data
data <- data[,list(id,class,t,count,desired,Roll.Val)][order(id,class)]
data
id class t count desired Roll.Val
1: 1 A 2010-01-15 1 1 1
2: 1 A 2010-02-15 2 3 3
3: 1 B 2010-04-15 3 3 3
4: 1 B 2010-09-15 4 4 4
5: 2 A 2010-01-15 5 5 5
6: 2 B 2010-06-15 6 6 6
7: 2 B 2010-08-15 7 13 13
8: 2 B 2010-09-15 8 21 21