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2012 Jul 12
1
Modifying a list: what gets copied?
...a shallow copy or a deep copy. I believe the
following experiment isolates the difference:
options(digits = 2)
powers <- 4:6
n <- setNames(10 ^ powers, paste0("e", powers))
xs <- lapply(n, seq_len)
zs <- lapply(xs, list)
vector_u <- function(x) x[length(x) + 1L] <- 1L
list_u <- function(x) z$a <- 1L
library(microbenchmark)
microbenchmark(
vector_u(xs$e4),
vector_u(xs$e5),
vector_u(xs$e6),
list_u(zs$e4),
list_u(zs$e5),
list_u(zs$e6)
)
On my computer, I get
Unit: microseconds
expr min lq median uq max
1 list_u(zs$e4) 122...