How can I interpret dates returned from ggvis handle_click

Question

First experience of using handle_click

library(ggvis)
library(dplyr)

# create data.frame
counts <- c(1,2)
dates <- as.Date(c("2015-01-01","2015-01-02"))
df <- data.frame(count=counts,date=dates)


# function to view clicked data
getDate = function(data,location,session){
  if(is.null(data)) return(NULL)
  glimpse(data)
}

df %>% 
  ggvis(~date,~count) %>% 
  layer_points() %>% 
  handle_click(getDate)

This returns when clicking the first point

Observations: 1
Variables:
$ date  (dbl) 1.42007e+12
$ count (int) 1

TIA

Answer 1

The dates appear as milliseconds from the origin time which is considered to be 1970-01-01 00:00:00.

As you can see you can transform that back to your original date using:

> as.POSIXct(1.42007e+12/1000, origin='1970-01-01 00:00:00 GMT')
[1] "2014-12-31 23:53:20 GMT"

The error of 6minutes is due to a rounding error I suppose.

You could change your script to see the dates as they should appear like this:

# function to view clicked data
getDate = function(data,location,session){
  if(is.null(data)) return(NULL)
  #just added the below line in your code
  data$date <- as.Date(as.POSIXct((data$date)/1000, origin='1970-01-01 00:10:00 GMT'))
  glimpse(data)
}

df %>% 
  ggvis(~date,~count) %>% 
  layer_points() %>% 
  handle_click(getDate)

Which returns on click:

Observations: 1
Variables:
$ date  (date) 2015-01-01
$ count (dbl) 1