我想得到的是NA,1,2,3,4

lag Lag a Time Series
Description
Compute a lagged version of a time series, shifting the time base back by a given number of observations.
lag is a generic function; this page documents its default method.
Usage
lag(x, ...)
## Default S3 method:
lag(x, k = 1, ...)
Arguments
x A vector or matrix or univariate or multivariate time series
k The number of lags (in units of observations).
... further arguments to be passed to or from methods.

dplyr::lag(1:5)