#173 gnuplot inconsistency with time format

[sgasp]

As of 4.6 gnuplot manage seconds with doubles allowing to go beyond seconds.
It possible to print time up to µs with

gnuplot>print strftime("%H:%M:%.3S %d-%b-%Y",time(0.0))
12:04:32.875415 22-Sep-2014

however the timemft does not support telling there is µs.
Not sure this limitation on timemft is the source of the trouble I have, however it can.

Here the issue I have.

I have series of data that are expresses by time and data
time is HH::MM::SS.ssssss
data is a number

Let's consider this data series as an example

12:31:01.354684 5
12:31:01.489654 20
12:31:01.579654 30
12:31:01.687654 20
12:31:01.707654 5

and this gnuplot commands

set xdata time
set timefmt "%H:%M:%S"
set xtics format "%H:%M:%.6S"
data="./data"
set table
plot data using 1:2

that will gives this output below

# Curve 0 of 1, 5 points
# Curve title: "data using 1:2"
# x y type
"12:31:01.354000"  5  i
"12:31:01.489000"  20  i
"12:31:01.579000"  30  i
"12:31:01.687000"  20  i
"12:31:01.707000"  5  i

1st my precision is truncated to ms, this is as per documentation, however print strftime("%H:%M:%.3S %d-%b-%Y",time(0.0)) gives up to µs, so I think it would be better to support µs every where.

Now in my case I want my T0 to be 00:00:00.000000.

So I want to substract the time found on my 1st raw when ploting.

The trick I use (I do not want to sues systeme command as I need my gnplot command files to work on any OS) is

plot data every ::0:0:0:1 using (t0=$1):2 with lines

that gives the output

# Curve 0 of 1, 1 points
# Curve title: "data every ::0:0:0:1 using (t0=$1):2"
# x y type
"00:00:12.000000"  5  i

Strange considering my data serie

I would think that $1 is the first column/first row data

but it is not, it is converted to a float not reprsenting a time data so I cannot substract it from a time.

I tried also

gnuplot>  plot data every ::0:0:0:1 using (t0=strftime("%H:%M:%.6S",$1)):2 with lines

This gives the same result

# Curve 0 of 1, 1 points
# Curve title: "data every ::0:0:0:1 using (t0=strftime("%H:%M:%.6S",$1)):2"
# x y type
"00:00:12.000000"  5  i

If I want to plot using my t0 variable I got this

plot data using ($1-t0):2
Warning: empty x range [0:0], adjusting to [-1:1]

# Curve 0 of 1, 5 points
# Curve title: "data using ($1-t0):2"
# x y type
"00:00:00.000000"  5  i
"00:00:00.000000"  20  i
"00:00:00.000000"  30  i
"00:00:00.000000"  20  i
"00:00:00.000000"  5  i

All my time are equal to 0

[Ethan Merritt]

Ticket moved from /p/gnuplot/bugs/1484/

[Karl Ratzsch]

Accessing an x column with time data via $1 (or column(1)) seems to not work (bug?), but you can use this:

plot data ev ::::0 using (t0=strptime("%H:%M:%S",stringcolumn(1))):2; print t0

In gp5 (and windows gp464 also, btw.) this even gives you dates with microsecond resolution.

P.S. You used strftime(), that takes number of seconds and returns a date string.

[Karl Ratzsch]

P.S. As of gp5, the function timecolumn() supports supplying a format string, so you won´t even need "set xdata time"/"set timefmt" any more.

plot $data using (t0=timecolumn(1,"%H:%M:%S")):2; print t0