Takes a numeric vector and will return the velocity of that vector.

## Details

Takes a numeric vector and will return the velocity of that vector. The velocity of a time series is computed by taking the first difference, so $$x_t - x_t1$$

This function can be used on it's own. It is also the basis for the function
`ts_velocity_augment()`

.

## See also

Other Vector Function:
`ts_acceleration_vec()`

## Examples

```
suppressPackageStartupMessages(library(dplyr))
len_out = 25
by_unit = "month"
start_date = as.Date("2021-01-01")
data_tbl <- tibble(
date_col = seq.Date(from = start_date, length.out = len_out, by = by_unit),
a = rnorm(len_out),
b = runif(len_out)
)
vec_1 <- ts_velocity_vec(data_tbl$b)
plot(data_tbl$b)
lines(data_tbl$b)
lines(vec_1, col = "blue")
```