```
a <- data.frame(x = 1:10, y = rnorm(10))
b <- data.frame(x = 1:10, y = rnorm(10))
endoapply(a, function(x) (x - mean(x))/sd(x))
mendoapply(function(e1, e2) (e1 - mean(e1)) * (e2 - mean(e2)), a, b)
x <- list(a=11:13, b=26:21, c=letters)
y <- list(-(5:1), c("foo", "bar"), 0.25)
pc(x, y)
library(IRanges)
x <- IntegerList(a=11:13, b=26:21, c=31:36, d=4:2)
y <- NumericList(-(5:1), 1:2, numeric(0), 0.25)
pc(x, y)
Reduce("+", x)
Filter(is.unsorted, x)
pos1 <- Position(is.unsorted, x)
stopifnot(identical(Find(is.unsorted, x), x[[pos1]]))
pos2 <- Position(is.unsorted, x, right=TRUE)
stopifnot(identical(Find(is.unsorted, x, right=TRUE), x[[pos2]]))
y <- x * 1000L
Map("c", x, y)
```

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