作者:靖憐兵役_523 | 来源:互联网 | 2023-02-02 14:46
1> talat..:
另一种方法是
c(t(sapply(-c:c, `+`, v)))
#[1] -2 -1 0 1 2 3 4 7 8 9 10 11 12 13 19 20 21 22 23 24 25
这对于大型v向量更有效,因为sapply循环只迭代-c:c
而不是每个元素v
.一个简单的比较表明:
set.seed(1)
v <- sample(1e6)
system.time(unlist( Map(`:`, v-c, v+c))) # akrun 1
# User System verstrichen
# 1.518 0.067 1.595
system.time(c(sapply(v, function(x) (x-c):(x+c)))) # akrun 2
# User System verstrichen
# 1.564 0.074 1.652
system.time(c(t(sapply(-c:c, '+', v)))) # docendo
# User System verstrichen
# 0.082 0.024 0.106
system.time(c(mapply(seq, v-c, v+c))) # 989
# User System verstrichen
# 7.132 0.123 7.292