Difference between c() and append()

 append() can be used instead of c(), but it is not recommended as c() is much more rapid than append():

> microbenchmark({m <- c(0, c(0, 3))}, times = 1E6)

Unit: nanoseconds

                       expr min  lq     mean median  uq     max neval

 {     m <- c(0, c(0, 3)) } 288 349 450.4081    355 393 6536440 1e+06

> microbenchmark({m <- append(0, append(0, 3))}, times = 1E6)

Unit: microseconds

                                 expr   min    lq     mean median    uq      max neval

 {     m <- append(0, append(0, 3)) } 1.488 1.763 2.178313  1.868 2.033 12825.54 1e+06

However, append() has one option more: 

x <- c(10,8,20)

c(x, 6) # always adds to the end

# [1] 10 8 20 6

append(x, 6, after = 2)

# [1] 10  8  6 20

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