Create count per item by year/decade

Question

I have data in a data.table that is as follows:

> x<-df[sample(nrow(df), 10),]
> x      

>                   Importer                 Exporter               


        

Answer 1

I think with will work with aggregate in base R:

my.data <- read.csv(text = '
        Importer,             Exporter,           Date
         Ecuador,       United Kingdom,     2004-01-13
          Mexico,        United States,     2013-11-19
       Australia,        United States,     2006-08-11
   United States,        United States,     2009-05-04
           India,        United States,     2007-07-16
       Guatemala,            Guatemala,     2014-07-02
          Israel,               Israel,     2000-02-22
           India,        United States,     2014-02-11
            Peru,                 Peru,     2007-03-26
          Poland,               France,     2014-09-15
', header = TRUE, stringsAsFactors = TRUE, strip.white = TRUE)

my.data$my.Date <- as.Date(my.data$Date, format = "%Y-%m-%d")

my.data <- data.frame(my.data,
                 year  = as.numeric(format(my.data$my.Date, format = "%Y")),
                 month = as.numeric(format(my.data$my.Date, format = "%m")),
                 day   = as.numeric(format(my.data$my.Date, format = "%d")))

my.data$my.decade <- my.data$year - (my.data$year %% 10)

importer.count <- with(my.data, aggregate(cbind(count = Importer) ~ my.decade + Importer, FUN = function(x) { NROW(x) }))
exporter.count <- with(my.data, aggregate(cbind(count = Exporter) ~ my.decade + Exporter, FUN = function(x) { NROW(x) }))

colnames(importer.count) <- c('my.decade', 'country', 'importer.count')
colnames(exporter.count) <- c('my.decade', 'country', 'exporter.count')

my.counts <- merge(importer.count, exporter.count, by = c('my.decade', 'country'), all = TRUE)

my.counts$importer.count[is.na(my.counts$importer.count)] <- 0
my.counts$exporter.count[is.na(my.counts$exporter.count)] <- 0

my.counts

#    my.decade        country importer.count exporter.count
# 1       2000      Australia              1              0
# 2       2000        Ecuador              1              0
# 3       2000          India              1              0
# 4       2000         Israel              1              1
# 5       2000           Peru              1              1
# 6       2000  United States              1              3
# 7       2000 United Kingdom              0              1
# 8       2010      Guatemala              1              1
# 9       2010          India              1              0
# 10      2010         Mexico              1              0
# 11      2010         Poland              1              0
# 12      2010  United States              0              2
# 13      2010         France              0              1