The R Project SVN – R – Diff – /trunk/src/library/base/man/Extract.data.frame.Rd



  \code{[[} are used with a single vector index (\code{x[i]} or
  \code{x[[i]]}), they index the data frame as if it were a list.  In
  this usage a \code{drop} argument is ignored, with a warning.
 
  There is no \code{data.frame} method for \code{$}, so \code{x$name}
  uses the default method which treats \code{x} as a list (with partial
  matching of column names if the match is unique, see
  \code{\link{Extract}}).  The replacement method (for \code{$}) checks
  \code{value} for the correct number of rows, and replicates it if necessary.
 
  When \code{[} and \code{[[} are used with two indices (\code{x[i, j]}
  and \code{x[[i, j]]}) they act like indexing a matrix:  \code{[[} can
  only be used to select one element.  Note that for each selected

sw[4:5, 1:3] # select rows and columns
sw[1]        # a one-column data frame
sw[, 1, drop = FALSE]  # the same
sw[, 1]      # a (unnamed) vector
sw[[1]]      # the same
sw$Fert      # the same (possibly w/ warning, see ?Extract)
 
sw[1,]       # a one-row data frame
sw[1,, drop = TRUE]  # a list
 
sw["C", ] # partially matches

sw["new1"] <- LETTERS[1:5]   # adds a character column
sw[["new2"]] <- letters[1:5] # ditto
sw[, "new3"] <- LETTERS[1:5] # ditto
sw$new4 <- 1:5
sapply(sw, class)
sw$new  # -> NULL: no unique partial match
sw$new4 <- NULL              # delete the column
sw
sw[6:8] <- list(letters[10:14], NULL, aa = 1:5)
# update col. 6, delete 7, append
sw

The R Project SVN R

(root)/trunk/src/library/base/man/Extract.data.frame.Rd – Rev 76103 → 76118

Rev 76103		Rev 76118
Line 51...		Line 51...
51	`\code{[[} are used with a single vector index (\code{x[i]} or`	51	`\code{[[} are used with a single vector index (\code{x[i]} or`
52	`\code{x[[i]]}), they index the data frame as if it were a list. In`	52	`\code{x[[i]]}), they index the data frame as if it were a list. In`
53	`this usage a \code{drop} argument is ignored, with a warning.`	53	`this usage a \code{drop} argument is ignored, with a warning.`
54		54
55	`There is no \code{data.frame} method for \code{$}, so \code{x$name}`	55	`There is no \code{data.frame} method for \code{$}, so \code{x$name}`
56	`uses the default method which treats \code{x} as a list (with no partial`	56	`uses the default method which treats \code{x} as a list (with partial`
-		57	`matching of column names if the match is unique, see`
57	`matching of column names). The replacement method (for \code{$}) checks`	58	`\code{\link{Extract}}). The replacement method (for \code{$}) checks`
58	`\code{value} for the correct number of rows, and replicates it if necessary.`	59	`\code{value} for the correct number of rows, and replicates it if necessary.`
59		60
60	`When \code{[} and \code{[[} are used with two indices (\code{x[i, j]}`	61	`When \code{[} and \code{[[} are used with two indices (\code{x[i, j]}`
61	`and \code{x[[i, j]]}) they act like indexing a matrix: \code{[[} can`	62	`and \code{x[[i, j]]}) they act like indexing a matrix: \code{[[} can`
62	`only be used to select one element. Note that for each selected`	63	`only be used to select one element. Note that for each selected`
Line 161...		Line 162...
161	`sw[4:5, 1:3] # select rows and columns`	162	`sw[4:5, 1:3] # select rows and columns`
162	`sw[1] # a one-column data frame`	163	`sw[1] # a one-column data frame`
163	`sw[, 1, drop = FALSE] # the same`	164	`sw[, 1, drop = FALSE] # the same`
164	`sw[, 1] # a (unnamed) vector`	165	`sw[, 1] # a (unnamed) vector`
165	`sw[[1]] # the same`	166	`sw[[1]] # the same`
-		167	`sw$Fert # the same (possibly w/ warning, see ?Extract)`
166		168
167	`sw[1,] # a one-row data frame`	169	`sw[1,] # a one-row data frame`
168	`sw[1,, drop = TRUE] # a list`	170	`sw[1,, drop = TRUE] # a list`
169		171
170	`sw["C", ] # partially matches`	172	`sw["C", ] # partially matches`
Line 189...		Line 191...
189	`sw["new1"] <- LETTERS[1:5] # adds a character column`	191	`sw["new1"] <- LETTERS[1:5] # adds a character column`
190	`sw[["new2"]] <- letters[1:5] # ditto`	192	`sw[["new2"]] <- letters[1:5] # ditto`
191	`sw[, "new3"] <- LETTERS[1:5] # ditto`	193	`sw[, "new3"] <- LETTERS[1:5] # ditto`
192	`sw$new4 <- 1:5`	194	`sw$new4 <- 1:5`
193	`sapply(sw, class)`	195	`sapply(sw, class)`
-		196	`sw$new # -> NULL: no unique partial match`
194	`sw$new4 <- NULL # delete the column`	197	`sw$new4 <- NULL # delete the column`
195	`sw`	198	`sw`
196	`sw[6:8] <- list(letters[10:14], NULL, aa = 1:5)`	199	`sw[6:8] <- list(letters[10:14], NULL, aa = 1:5)`
197	`# update col. 6, delete 7, append`	200	`# update col. 6, delete 7, append`
198	`sw`	201	`sw`