## ----echo=FALSE, file='_translation_links.R'------------------------------------------------------
# build a link list of alternative languages (may be character(0))
# idea is to look like 'Other languages: en | fr | de'
.write.translation.links <- function(fmt) {
    url = "https://rdatatable.gitlab.io/data.table/articles"
    path = dirname(knitr::current_input(TRUE))
    if (basename(path) == "vignettes") {
      lang = "en"
    } else {
      lang = basename(path)
      path = dirname(path)
    }
    translation = dir(path,
      recursive = TRUE,
      pattern = glob2rx(knitr::current_input(FALSE))
    )
    transl_lang = ifelse(dirname(translation) == ".", "en", dirname(translation))
    block = if (!all(transl_lang == lang)) {
      linked_transl = sprintf("[%s](%s)", transl_lang, file.path(url, sub("(?i)\\.Rmd$", ".html", translation)))
      linked_transl[transl_lang == lang] = lang
      sprintf(fmt, paste(linked_transl, collapse = " | "))
    } else ""
    knitr::asis_output(block)
}

## ----echo = FALSE, message = FALSE----------------------------------------------------------------
require(data.table)
knitr::opts_chunk$set(
  comment = "#",
    error = FALSE,
     tidy = FALSE,
    cache = FALSE,
 collapse = TRUE)
.old.th = setDTthreads(1)

## ----echo = FALSE---------------------------------------------------------------------------------
options(width = 100L)

## -------------------------------------------------------------------------------------------------
flights <- fread("flights14.csv")
head(flights)
dim(flights)

## ----keyed_operations-----------------------------------------------------------------------------
DT = data.table(a = c(TRUE, FALSE), b = 1:2)
setkey(DT, a)                # Set key, reordering DT
DT[.(TRUE)]                  # 'on' is optional; if omitted, the key is used

## ----unkeyed_operations---------------------------------------------------------------------------
DT = data.table(a = c(TRUE, FALSE), b = 1:2)
setindex(DT, a)              # Set index only (no reorder)
DT[.(TRUE), on = "a"]        # 'on' is required

## -------------------------------------------------------------------------------------------------
setindex(flights, origin)
head(flights)

## alternatively we can provide character vectors to the function 'setindexv()'
# setindexv(flights, "origin") # useful to program with

# 'index' attribute added
names(attributes(flights))

## -------------------------------------------------------------------------------------------------
indices(flights)

setindex(flights, origin, dest)
indices(flights)

## ----eval = FALSE---------------------------------------------------------------------------------
# ## not run
# setkey(flights, origin)
# flights["JFK"] # or flights[.("JFK")]

## ----eval = FALSE---------------------------------------------------------------------------------
# ## not run
# setkey(flights, dest)
# flights["LAX"]

## -------------------------------------------------------------------------------------------------
flights["JFK", on = "origin"]

## alternatively
# flights[.("JFK"), on = "origin"] (or)
# flights[list("JFK"), on = "origin"]

## -------------------------------------------------------------------------------------------------
setindex(flights, origin)
flights["JFK", on = "origin", verbose = TRUE][1:5]

## -------------------------------------------------------------------------------------------------
flights[.("JFK", "LAX"), on = c("origin", "dest")][1:5]

## -------------------------------------------------------------------------------------------------
flights[.(origin = "JFK", dest = "LAX"), on = c("origin", "dest")]

## -------------------------------------------------------------------------------------------------
flights[.("LGA", "TPA"), .(arr_delay), on = c("origin", "dest")]

## -------------------------------------------------------------------------------------------------
flights[.("LGA", "TPA"), .(arr_delay), on = c("origin", "dest")][order(-arr_delay)]

## -------------------------------------------------------------------------------------------------
flights[.("LGA", "TPA"), max(arr_delay), on = c("origin", "dest")]

## -------------------------------------------------------------------------------------------------
# get all 'hours' in flights
flights[, sort(unique(hour))]

## -------------------------------------------------------------------------------------------------
flights[.(24L), hour := 0L, on = "hour"]

## -------------------------------------------------------------------------------------------------
flights[, sort(unique(hour))]

## -------------------------------------------------------------------------------------------------
ans <- flights["JFK", max(dep_delay), keyby = month, on = "origin"]
head(ans)

## -------------------------------------------------------------------------------------------------
flights[c("BOS", "DAY"), on = "dest", mult = "first"]

## -------------------------------------------------------------------------------------------------
flights[.(c("LGA", "JFK", "EWR"), "XNA"), on = c("origin", "dest"), mult = "last"]

## -------------------------------------------------------------------------------------------------
flights[.(c("LGA", "JFK", "EWR"), "XNA"), mult = "last", on = c("origin", "dest"), nomatch = NULL]

## -------------------------------------------------------------------------------------------------
set.seed(1L)
dt = data.table(x = sample(1e5L, 1e7L, TRUE), y = runif(100L))
print(object.size(dt), units = "Mb")

## -------------------------------------------------------------------------------------------------
## have a look at all the attribute names
names(attributes(dt))

## run thefirst time
(t1 <- system.time(ans <- dt[x == 989L]))
head(ans)

## secondary index is created
names(attributes(dt))

indices(dt)

## -------------------------------------------------------------------------------------------------
## successive subsets
(t2 <- system.time(dt[x == 989L]))
system.time(dt[x %in% 1989:2012])

## ----echo=FALSE-----------------------------------------------------------------------------------
setDTthreads(.old.th)