Add function time_axis()

DESCRIPTION

@@ -1,6 +1,6 @@
 Package: broman
-Version: 0.81-1
-Date: 2024-02-05
+Version: 0.81-2
+Date: 2024-05-03
 Title: Karl Broman's R Code
 Description: Miscellaneous R functions, including functions related to
     graphics (mostly for base graphics), permutation tests, running

NAMESPACE

@@ -66,6 +66,7 @@ export(strwidth2lines)
 export(strwidth2xlim)
 export(switchv)
 export(theme_karl)
+export(time_axis)
 export(trap)
 export(triarrow)
 export(trigrid)

NEWS.md

@@ -1,10 +1,12 @@
 Revision history for the R/broman package
 -----------------------------------------
 
-## Version 0.81-1, 2024-02-05
+## Version 0.81-2, 2024-05-03
 
 - Small change to documentation for `objectsizes()` (Mb -> MB)
 
+- Added function `time_axis()` for helping set up axis labels for date/times.
+
 
 ## Version 0.80, 2022-07-08
 

R/time_axis.R

@@ -0,0 +1,40 @@
+#' Set up a time-based axis
+#'
+#' Set up a time-based axis for base graphics
+#'
+#' @param times A vector of date/times that will be plotted
+#'
+#' @param n Number of values to use in axis
+#'
+#' @return A data frame with the numeric values to plot plus labels to use.
+#'
+#' @export
+
+time_axis <-
+    function(times, n=8)
+{
+    if(!("POSIXct" %in% class(times) || "POSIXt" %in% class(times))) {
+        stop("times should be a vector of date/times")
+    }
+
+    prettyx <- pretty(times, n=n)
+
+    r <- range(as.numeric(times))
+    dr <- diff(r)
+    # determine range
+    if(dr < 70) { # seconds
+        labels <- format(prettyx, format="%S")
+    }
+    else if(dr < 60*70) { # minutes
+        labels <- format(prettyx, format="%H:%M")
+    }
+    else if(dr < 60*60*26) { # hours
+        labels <- format(prettyx, format="%H:%M")
+    }
+    else { # days
+        labels <- format(prettyx, format="%Y-%m-%d")
+    }
+
+    # return vector of "pretty" times + labels
+    data.frame(x=prettyx, label=labels)
+}