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#1368 stripchart can't extend with custom labels
If I create a stripchart with custom labels:
set s [Plotchart::createStripchart .c {0 10 ""} {0 10 1} -xlabels {a b c}]
I then get an error when I try to plot the final point in this data:
foreach {x y} {0 0 2 5 5 2 9 9 12 10} {
$s plot a $x $y
}
The issue appears to be that the tick interval is an empty string, which is necessary to get the custom x-axis labels to display. (I ran across this issue when providing user support in http://stackoverflow.com/q/16658143/301832 when changing from an xyplot to a stripchart.)
As Donal informed me, the original purpose was to display a stripchart with time (or date/time) instead of numbers along the x-axis.
Given that non-numeric custom labels are drawn at regular spacing, defined
by their number, the concept is not a good match with stripcharts: stripcharts
need to add new labels when the x-value increases beyond the upper limit.
The solution I will implement is:
- Give a proper error message about custom labels with stripcharts
- Implement an option -timeformat (and an option -gmt) so that the x-axis
gets labelled with dates/times instead of numbers.
That option will allow generating new labels, just as with ordinary numbers.
The option -gmt is meant to control daylight saving time surprises
Fixed as of version 2.1.1:
Use the -timeformat option to display date/time labels in a stripchart.
See the example below for the use of these options or the documentation:
package require Plotchart
pack [canvas .c]
#
# New code:
# Note that we need to present the x values as clock seconds
# The increment is equal to 2 hours (2*3600 seconds)
#
set start [clock scan "0:00"]
set stop [clock scan "10:00"]
set s [Plotchart::createStripchart .c [list $start $stop 7200] {0 10 1} -timeformat "%H:%M"]
foreach {x y} {0 0 2 5 5 2 9 9 12 10} {
set x [expr {$start + 3600 * $x}] ;# Convert hour to clock seconds
$s plot a $x $y
}