changed directory

Author: venom1204

man/data.table.Rd

@@ -350,6 +350,24 @@ setkeyv(kDT,v)                        # same
 haskey(kDT)                           # TRUE
 key(kDT)                              # "x"
 
+# Keyed subsetting (no 'on' needed)
+setkey(kDT, x)                        # Set a key on column 'x'
+kDT[.("a")]                            # Returns all rows where x = "a"
+
+# Indexed subsetting (requires 'on')
+setindex(kDT, x)                       # Set an index on column 'x'
+kDT[.("b"), on = "x"]                  # Works, returns all rows where x = "b" (for detailed explanation visit setkey.rd)
+# kDT[.("b")]                          # this will throw error
+
+# single and multiple indices
+# index on a single column ('y')
+setindex(kDT, y)
+indices(kDT)
+
+# multi-column index
+setindexv(kDT, list("x", c("x", "y")))
+indices(kDT)                           # Shows an index on 'x' and a composite index on '(x,y)'
+
 # fast *keyed* subsets
 kDT["a"]                              # subset-as-join on *key* column 'x'
 kDT["a", on="x"]                      # same, being explicit using 'on=' (preferred)

man/setkey.Rd

@@ -155,23 +155,6 @@ setindex(DT, A)
 setindex(DT, B)
 indices(DT)           # get indices single vector
 indices(DT, vectors = TRUE) # get indices list
-
-# Keyed subsetting (no 'on' needed)
-DT = data.table(A=5:1,B=letters[5:1])
-setkey(DT, B)
-DT[.("e")]  # Returns row where B = "e"
-
-# Indexed subsetting (requires 'on')
-DT = data.table(A=5:1,B=letters[5:1])
-setindex(DT, B)
-DT[.("e"), on = "B"]  # Works
-# DT[.("e")]           # Would error (missing 'on')
-
-DT <- data.table(a = c(1,2,1,2), b = c("x", "x", "y", "y"), val = 1:4)
-# Set an index on a single column
-setindex(DT, a)
-# Set multiple indices at once using setindexv
-setindexv(DT, list("a", c("a", "b")))
 
 # Setting multiple indices at once
 DT = data.table(A = 5:1, B = letters[5:1], C = 10:6)