为什么使用names()函数时*apply返回命名对象而不是值的向量?

# pass names and values
f <- function(name, value)  sprintf("%s: %d", name, value)
mapply(f, names(vec), vec)
##      a      b 
## "a: 1" "b: 2" 

# pass names but look up values
f2 <- function(name) sprintf("%s: %d", name, vec[name])
sapply(names(vec), f2)
##      a      b 
## "a: 1" "b: 2" 

# pass index and lookup both names and values
f3 <- function(i) sprintf("%s: %d", names(vec)[i], vec[i])
sapply(seq_along(vec), f3)
##      a      b 
## "a: 1" "b: 2" 

# if values are unique can pass values and look up names
f4 <- function(value) sprintf("%s: %d", names(vec)[match(value, vec)], value)
sapply(vec, f4)
##      a      b 
## "a: 1" "b: 2" 

# convert to a 2 column data frame w names (ind) and values  
spl <- split(stack(vec), seq_along(vec))  
sapply(spl, with, sprintf("%s: %d", ind, values))
##      a      b 
## "a: 1" "b: 2"