Reduce a data.frame so that the (primary) key column contains only unique entries and other columns pertaining to that entry are combined into semicolon-separated values into a single row/observation.
# S4 method for data.frame
reduce(x, key, sep = ";")A data.frame.
The column name (currenly only one is supported) to be used as primary key.
The separator. Default is ;.
A reduced data.frame.
An important side-effect of reducing a data.frame is that all
columns other than the key are converted to characters when they
are collapsed to a semi-column separated value (even if only one
value is present) as soon as one observation of transformed.
dfr <- data.frame(A = c(1, 1, 2),
B = c("x", "x", "z"),
C = LETTERS[1:3])
dfr
#> A B C
#> 1 1 x A
#> 2 1 x B
#> 3 2 z C
dfr2 <- reduce(dfr, key = "A")
dfr2
#> A B C
#> 1 1 x;x A;B
#> 2 2 z C
## column A used as key is still num
str(dfr2)
#> 'data.frame': 2 obs. of 3 variables:
#> $ A: num 1 2
#> $ B: chr "x;x" "z"
#> $ C: chr "A;B" "C"
dfr3 <- reduce(dfr, key = "B")
dfr3
#> A B C
#> 1 1;1 x A;B
#> 2 2 z C
## A is converted to chr; B remains factor
str(dfr3)
#> 'data.frame': 2 obs. of 3 variables:
#> $ A: chr "1;1" "2"
#> $ B: chr "x" "z"
#> $ C: chr "A;B" "C"
dfr4 <- data.frame(A = 1:3,
B = LETTERS[1:3],
C = c(TRUE, FALSE, NA))
## No effect of reducing, column classes are maintained
str(reduce(dfr4, key = "B"))
#> 'data.frame': 3 obs. of 3 variables:
#> $ A: int 1 2 3
#> $ B: chr "A" "B" "C"
#> $ C: logi TRUE FALSE NA