Shift to the middle of each interval

After thickening all the values are either shifted to the first or the last value of their interval. This function creates a vector from x, with the values shifted to the (approximate) center of the interval. This can give a more accurate picture of the aggregated data when plotting.

center_interval(x, shift = c("up", "down"), interval = NULL)

Arguments

x	A vector of class Date, POSIXct or POSIXlt.
shift	"up" or "down".
interval	The interval to be used for centering. If NULL, get_interval will be applied on x.

Value

Vector of the same class as x, with the values shifted to the (approximate) center.

Details

The interval will be translated to number of days when x is of class Date, or number of seconds when x is of class POSIXt. For months and quarters this will be the average length of the interval. The translated units divided by two will be added by or subtracted from each value of x.

Examples

library(dplyr)
#> 
#> Attaching package: ‘dplyr’
#> The following object is masked from ‘package:testthat’:
#> 
#>     matches
#> The following objects are masked from ‘package:stats’:
#> 
#>     filter, lag
#> The following objects are masked from ‘package:base’:
#> 
#>     intersect, setdiff, setequal, union
library(ggplot2)
#> Registered S3 methods overwritten by 'ggplot2':
#>   method         from 
#>   [.quosures     rlang
#>   c.quosures     rlang
#>   print.quosures rlang
plot_set <- emergency %>%
  thicken("hour", "h") %>%
  count(h) %>%
  head(24)

ggplot(plot_set, aes(h, n)) + geom_col()

plot_set %>%
  mutate(h_center = center_interval(h)) %>%
  ggplot(aes(h_center, n)) + geom_col()