R COMMANDS AND TRICKS

R commands, shortcuts, and tricks I find to be elegant or tend to forget.


1. replace values in a vector

    x <- c("a", "b", "a", "o", "b")
    y <- c(a = "apple", b = "bannana", o = "orange")[x]

    > y
    #       a         b         a         o         b
    # "apple" "bannana"   "apple"  "orange" "bannana"

2. replace values in a vector (reversed dictionary)

    x <- c("a", "b", "a", "o", "b")
    d <- c(apple = "a", bannana = "b", orange = "o")
    y <- names(d)[match(x, d)]

    > y
    # [1] "apple"   "bannana" "apple"   "orange"  "bannana"

3. replace intervals with group names

    x <- c(2, 16, 88, 15, 33, 1, 21)
    d <- c(baby = 0, toddler = 2, child = 6, teen = 12, adult = 18, senior = 65)
    y <- names(d)[findInterval(x, d)]

    > y
    # [1] "toddler" "teen"    "senior"  "teen"    "adult"   "baby"    "adult"

4. repeat string values multiple times

    x <- c("-", "o", "-")
    y <- strrep(x, c(4, 2, 4))

    > y
    # [1] "----" "oo" "----"

5. generate equally distributed factor levels

    y <- gl(2, 4, labels = c("male", "female"))

    > y
    # [1] male   male   male   male   female female female female
    # Levels: male female

6. get interactions between two factors and their levels

   x <- factor(c("M", "F"))
   y <- factor(c("young", "old"))

   > x:y
   # [1] M:young F:old
   # Levels: F:old F:young M:old M:young

7. subtract means from each column of a matrix

   x <- data.matrix(iris)
   x <- x - colMeans(x)[col(x)]
   x <- x / apply(x, 2, sd)[col(x)]

8. order/sort each row of a matrix

   x <- data.matrix(iris)
   x <- matrix(col(x)[order(row(x), x)], nrow=nrow(x), byrow=TRUE)
   x <- matrix(x[order(row(x), x)], nrow=nrow(x), byrow=TRUE)