simplifiy and rebuild overview vignette

Author: bgctw

vignettes/overview.Rmd

@@ -159,18 +159,20 @@ abline( v = trunc(dateSeq[1], units = "days") + c(sunrise,sunset)*3600L )
 ```
 
 Function `getHoursAheadOfUTC` provides the integer timeZone argument 
-of a timestamp, required other functions of the package.
+of a timestamp, required by other functions of the package.
 Similarly, `getFractionalHours` provides fractional hours after midnight of
 a timestamp.
 
 ```{r}
 #around daylight saving time step in Central European time
-tzBack <- Sys.getenv("TZ"); Sys.setenv(TZ = "Europe/Berlin") 
-  t1 <- as.POSIXct("2018-10-28 01:30")
-  (dateSeq <- seq(t1, by = "30 min", length.out = 6))
-  (hoursAhead <- getHoursAheadOfUTC(dateSeq))
-  (facHours <- getFractionalHours(dateSeq))
-Sys.setenv(TZ = tzBack)
+t1 <- as.POSIXct("2018-10-28 01:30", tz = "Europe/Berlin")
+datesCET <- seq(t1, by = "30 min", length.out = 6)
+datesUTC <- as.POSIXct(datesCET, tz = "UTC")
+#
+hoursAheadOfUTC <- getHoursAheadOfUTC(datesCET)
+fracHours <- getFractionalHours(datesCET)
+#
+data.frame(datesUTC, datesCET, hoursAheadOfUTC, fracHours)
 ```
 
 <!-- 

vignettes/overview.md

@@ -135,21 +135,19 @@ a timestamp, required other functions of the package. Similarly,
 timestamp.
 
     #around daylight saving time step in Central European time
-    tzBack <- Sys.getenv('TZ'); Sys.setenv(TZ = "Europe/Berlin") 
-      t1 <- as.POSIXct("2018-10-28 01:30")
-      (dateSeq <- seq(t1, by = "30 min", length.out = 6))
-
-    ## [1] "2018-10-28 01:30:00 CEST" "2018-10-28 02:00:00 CEST" "2018-10-28 02:30:00 CEST" "2018-10-28 02:00:00 CET"  "2018-10-28 02:30:00 CET"  "2018-10-28 03:00:00 CET"
-
-      (hoursAhead <- getHoursAheadOfUTC(dateSeq))
-
-    ## [1] 2 2 2 1 1 1
-
-      (facHours <- getFractionalHours(dateSeq))
-
-    ## [1] 1.5 2.0 2.5 3.0 3.5 4.0
-
-    Sys.setenv(TZ = tzBack)
+    t1 <- as.POSIXct("2018-10-28 01:30", tz = "Europe/Berlin")
+    dateSeq <- seq(t1, by = "30 min", length.out = 6)
+    hoursAheadOfUTC <- getHoursAheadOfUTC(dateSeq)
+    fracHours <- getFractionalHours(dateSeq)
+    data.frame(dateSeq, hoursAheadOfUTC, fracHours)
+
+    ##               dateSeq hoursAheadOfUTC fracHours
+    ## 1 2018-10-28 01:30:00               2       1.5
+    ## 2 2018-10-28 02:00:00               2       2.0
+    ## 3 2018-10-28 02:30:00               2       2.5
+    ## 4 2018-10-28 02:00:00               1       3.0
+    ## 5 2018-10-28 02:30:00               1       3.5
+    ## 6 2018-10-28 03:00:00               1       4.0
 
 <!-- 
 See the [package vignettes](https://github.com/bgctw/solartime/tree/master/vignettes) (*.md) for further examples.