For displaying the result after an assignment, instead of printing the variable explicitly on a new line:
x <- 1:10
x
## [1] 1 2 3 4 5 6 7 8 9 10
The assignment can be surrounded with parenthesis:
(x <- 1:10)
## [1] 1 2 3 4 5 6 7 8 9 10
For initiating empty variables, instead of assigning them one by one:
x <- numeric(10)
y <- numeric(10)
z <- numeric(10)
x
## [1] 0 0 0 0 0 0 0 0 0 0
They all can be assigned in a single line:
x <- y <- z <- numeric(10)
x
## [1] 0 0 0 0 0 0 0 0 0 0
For assigning a value based on logical condition, instead of making an assignment within an if statement:
if(rnorm(1) > 0) {
result <- "positive"
} else {
result <- "negative"
}
The statement itself can be assigned to a variable directly:
result <- if(rnorm(1) > 0) "positive" else "negative"
For reversing the direction of elements within a vector, instead of selecting the elements in decreasing order:
x <- 1:10
x[length(x):1]
## [1] 10 9 8 7 6 5 4 3 2 1
A short rev() function can be used:
x <- 1:10
rev(x)
## [1] 10 9 8 7 6 5 4 3 2 1
To select the last element of a vector, instead of specifying the index of the last element:
rivers[length(rivers)]
## [1] 1770
A tail() function can be used:
tail(rivers, 1)
## [1] 1770
For selecting elements from a nested list, instead of stacking brackets:
a <- list(3, list(8, list(0, 5)))
a[[2]][[2]][[1]]
## 0
A single vector of indices can be used:
a <- list(3, list(8, list(0, 5)))
a[[c(2,2,1)]]
## 0
For obtaining lengths of each element inside a list, instead of calling length() on each element:
xs <- list(1:10, 2, 3:4, letters, rivers)
sapply(xs, length)
## [1] 10 1 2 26 141
The lengths can be obtained by using a special function:
xs <- list(1:10, 2, 3:4, letters, rivers)
lengths(xs)
## [1] 10 1 2 26 141
For checking which strings in a vector start with a specified prefix, instead of using grepl():
x <- c("something", "wholesome", "somebody")
grepl("^some", x)
## [1] TRUE FALSE TRUE
A simpler startsWith() function can be used instead:
x <- c("something", "wholesome", "somebody")
startsWith(x, "some")
## [1] TRUE FALSE TRUE
And equivalent function exists for looking at suffixes:
x <- c("something", "wholesome", "somebody")
endsWith(x, "some")
## [1] FALSE TRUE FALSE
For repeating extending a string by repeating it a specified number of times, instead of rep() and paste():
x <- c("ABABAB")
paste(rep(x, 3), collapse="")
## [1] "ABABABABABABABABAB"
A short dedicated function can be used:
strrep(x, 3)
## [1] "ABABABABABABABABAB"
For turning vector elements to NA, instead of regular replacement:
x <- c(2, 5, 9, 0)
x[c(2,4)] <- NA
x
## [1] 2 NA 9 NA
A special assignment function can be used:
x <- c(2, 5, 9, 0)
is.na(x) <- c(2, 4)
x
## [1] 2 NA 9 NA
Or, alternatively, using names:
x <- c(a=2, b=5, c=9, d=0)
is.na(x) <- c("b", "d")
x
## a b c d
## 2 NA 9 NA
For repeating expressions multiple times, instead of running a for loop or using sapply():
means <- numeric(10)
for(i in 1:10) {
means[i] <- mean(rnorm(20))
}
means
## [1] -0.10172177 0.54172359 0.25915355 -0.07303793 -0.17569846
## [6] 0.37802472 -0.39325875 0.07182746 0.04113407 -0.06892520
sapply(1:10, function(x) mean(rnorm(20)))
## [1] -0.10172177 0.54172359 0.25915355 -0.07303793 -0.17569846
## [6] 0.37802472 -0.39325875 0.07182746 0.04113407 -0.06892520
A dedicated replicate() function can be used:
replicate(10, mean(rnorm(20)))
## [1] -0.10172177 0.54172359 0.25915355 -0.07303793 -0.17569846
## [6] 0.37802472 -0.39325875 0.07182746 0.04113407 -0.06892520
For creating factors with equal number of levels, instead of repeating strings:
as.factor(rep(c("Child", "Man", "Woman"), each=3))
## [1] Child Child Child Man Man Man Woman Woman Woman
## Levels: Child Man Woman
A special gl() function can be used:
gl(3, 3, labels = c("Child", "Man", "Woman"))
## [1] Child Child Child Man Man Man Woman Woman Woman
## Levels: Child Man Woman
For replacing values in a vector, instead of doing multiple assignments:
x <- c("a", "b", "a", "c", "a", "b", "b")
x[x=="a"] <- "apple"
x[x=="b"] <- "bananna"
x[x=="c"] <- "cherry"
x
## [1] "apple" "bananna" "apple" "cherry" "apple" "bananna" "bananna"
The match() function can be used:
x <- c("a", "b", "a", "c", "a", "b", "b")
n <- c(apple="a", bananna="b", cherry="c")
names(n)[match(x, n)]
## [1] "apple" "bananna" "apple" "cherry" "apple" "bananna" "bananna"
And a similar strategy can be used for replacing interval regions using findInterval():
x <- c(2, 16, 88, 15, 33, 1, 21)
n <- c(baby=0, toddler=1, child=3, teen=12, adult=18, senior=65)
names(n)[findInterval(x, n)]
## [1] "toddler" "teen" "senior" "teen" "adult" "toddler" "adult"
For obtaining group-wise sums from a matrix or a data frame, instead of using aggregate():
aggregate(iris[,-5], list(iris[,5]), FUN=sum)
## Group.1 Sepal.Length Sepal.Width Petal.Length Petal.Width
## 1 setosa 250.3 171.4 73.1 12.3
## 2 versicolor 296.8 138.5 213.0 66.3
## 3 virginica 329.4 148.7 277.6 101.3
A special rowsum() function can be used:
rowsum(iris[,-5], iris[,5])
## Sepal.Length Sepal.Width Petal.Length Petal.Width
## setosa 250.3 171.4 73.1 12.3
## versicolor 296.8 138.5 213.0 66.3
## virginica 329.4 148.7 277.6 101.3
And for averages:
rowsum(iris[,-5], iris[,5]) / table(iris[,5])
## Sepal.Length Sepal.Width Petal.Length Petal.Width
## setosa 5.006 3.428 1.462 0.246
## versicolor 5.936 2.770 4.260 1.326
## virginica 6.588 2.974 5.552 2.026
For finding a column index holding the maximum value for each row, instead of using which.max():
apply(VADeaths, 1, which.max)
## 50-54 55-59 60-64 65-69 70-74
## 3 3 3 3 3
A special max.col() function can be used:
max.col(VADeaths)
## [1] 3 3 3 3 3
For constructing multi-line titles in plots, instead of combining strings with paste():
plot(1:10, main=paste("Title", "sub", sep="\n"), xlab=paste("index", "x", sep="\n"))
Titles can be specified by passing a vector of strings:
plot(1:10, main=c("Title", "sub"), xlab=c("Index", "x"))
For increasing the range of the axes within a plot, instead of computing limits manually:
x <- 1:10
y <- rnorm(10)
plot(x, y, xlim=range(x) + diff(range(x)) * c(-0.2, 0.2))
A dedicated function can be used:
x <- 1:10
y <- rnorm(10)
plot(x, y, xlim=extendrange(x, f=0.2))
Thanks to /u/morphicphicus from /r/rstats reddit thread for a reminder about (x <- y) print shortcut.