Recoding levels of factors

r

Solution

Here's one approach:

within(forStack, {
  A <- as.numeric(!A %in% tail(levels(A), 2))
  B <- as.numeric(!B %in% head(levels(B), 2))
})
#   AGE  BMI time A B      ID
# 1  59 23.8    0 1 1 9000099
# 2  69 29.8    0 0 0 9000296
# 3  71 22.7    0 1 1 9000622
# 4  56 32.4    0 1 1 9000798
# 5  72 30.7    0 1 1 9001104
# 6  75 23.5    0 0 0 9001400

The basic idea here is that `head` and `tail` both have an "`n`" argument that lets you specify how many values you want from the "head" and "tail" of your vector or dataset. That lets us easily grab `(96.4,100]` and `(100, Inf]` for vector A, and the relevant values for vector B.

`within` is a convenient way to dynamically replace the values in your `data.frame`.

Problem

I have following dataframe: ``` forStack AGE BMI time A B ID 1 59 23.8 0 (0,75] (4,14.9] 9000099 2 69 29.8 0 (96.4,100] (-Inf,0] 9000296 3 71 22.7 0 (75,89.3] (4,14.9] 9000622 4 56 32.4 0 (0,75] (14.9,68] 9000798 5 72 30.7 0 (0,75] (14.9,68] 9001104 6 75 23.5 0 (96.4,100] (0,4] 9001400 dput (forStack) structure(list(AGE = c(59, 69, 71, 56, 72, 75), BMI = c(23.8, 29.8, 22.7, 32.4, 30.7, 23.5), time = c(0, 0, 0, 0, 0, 0), A = structure(c(2L, 5L, 3L, 2L, 2L, 5L), .Label = c("(-Inf,0]", "(0,75]", "(75,89.3]", "(89.3,96.4]", "(96.4,100]", "(100, Inf]"), class = "factor"), B = structure(c(3L, 1L, 3L, 4L, 4L, 2L), .Label = c("(-Inf,0]", "(0,4]", "(4,14.9]", "(14.9,68]", "(68, Inf]"), class = "factor"), ID = c(9000099, 9000296, 9000622, 9000798, 9001104, 9001400 )), .Names = c("AGE", "BMI", "time", "A", "B", "ID"), row.names = c(NA, 6L), class = "data.frame") ``` Variables `A` and `B` are factors representing quartiles: ``` forStack$A [1] (0,75] (96.4,100] (75,89.3] (0,75] (0,75] (96.4,100] Levels: (-Inf,0] (0,75] (75,89.3] (89.3,96.4] (96.4,100] (100, Inf] forStack$B [1] (4,14.9] (-Inf,0] (4,14.9] (14.9,68] (14.9,68] (0,4] Levels: (-Inf,0] (0,4] (4,14.9] (14.9,68] (68, Inf] ``` I would like to recode `A` and `B` values to two-level factors as follows: For `A`, the upper factor levels `(96.4,100]` and `(100, Inf]` should be recoded as 0 level, other levels - as 1 level For `B` the the lowest factor levels `(-Inf,0]` and `(0,4]` should be recoded as 0 level, other levels - as 1 level Thus, the dataframe should look like: ``` forStack AGE BMI time A B ID 1 59 23.8 0 1 1 9000099 2 69 29.8 0 0 0 9000296 3 71 22.7 0 1 1 9000622 4 56 32.4 0 1 1 9000798 5 72 30.7 0 1 1 9001104 6 75 23.5 0 0 0 9001400 ``` What is the most efficient way to do it? Thank you very much in advance

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