plot all-missing variable together with another variable, yields no result

[karlmsmith]

Reported by @AnsleyManke on 28 Apr 2010 18:17 UTC
Reported by Marco Steinacher,
http://www.pmel.noaa.gov/maillists/tmap/ferret_users/fu_2010/msg00266.html

The behavior goes back to Ferret v5.81 at least.

He defines a variable which is all missing; from a variable in an ASCII file.

--- Contents of test.dat:
2000 0.0
2010 0.0
---

--- Example script:
file/var="year,data" "test.dat"

let var1 = data[d=1]
let var2 = if data[d=1] eq -1 then data[d=1]

plot var1        ! Works
plot var2        ! Works
list var1,var2   ! Works
plot var1,var2   ! Doesn't work!
---

The result is a blank plot window. If mode meta is set, the metafile converts to an invalid postscript file. If in gif mode, the gif file is just blank.

However, other similar examples work fine. Plotting missing and non-missing data from a netCDF file works fine:

yes? use coads_climatology
yes? plot/L=1 sst[y=0],sst[y=-88]   ! gives a good plot

Also user-defined variables do not behave this way. Here a valid plot is drawn.

yes? let v1 = x[i=1:5]
yes? let v2 = if v1 eq -1 then v1
yes? plot v1
yes? plot v2
yes? plot v1,v2

It seems to be the combination of the all-zero-value variable and the all-missing variable.

This fails to make a plot:

yes? let v1 = {0,0,0}
yes? let v2  = { , , }
yes? plot v1,v2

This does make a plot:

yes? let v1 = {10,10,10}
yes? let v2  = { , , }
yes? plot v1,v2

Migrated-From: http://dunkel.pmel.noaa.gov/trac/ferret/ticket/1736