Re: using gnuplot's "splot" and "every" commands on org-mode table data

[Paul Stansell <paulstansell@gmail.com>]

Hi Eric,

In your last example are you illustrating the case of a data file with
missing data?  Replacing ""s with blank space in your example doesn't
really break the plot, it's just that gnuplot interprets the first
column of data as

1
2
3
16

6
7
4
9

and the second as

2
4
8


16
8
4
2

Gnuplot has a specific setting for handling missing values.  It's
common in gnuplot to use '?' to signify a missing value (type "help
missing" at the gnuplot prompt).  If, in your last example, you
replace the missing values with '?' (without the quotes) and then type
in gnuplot

  set datafile missing "?"

and then plot the data with

  plot "data.txt" u 0:1, '' u 0:2

you'll see that gnuplot handles it properly.  Putting '?' in the
blanks cells of the org mode table in your last attachment and
plotting from within org mode gives a temporary data file containing
'"?"', which gnuplot also handles correctly as it must recognise "?"
(with the quotes) as being a missing value.

But org mode's behaviour of inserting "" in blank cells (instead of
actual blanks) does break the use of "every" in gnuplot which is
required by splot when plotting surfaces from data files (unless the
data files are in "matrix" format).  Also, inserting "" breaks the use
of gnuplot's "index" which expects two blank lines to separate data
sets in a single file, but I've never used this facility.

I noticed that org mode writes table values of 'nan' and 'NaN' without
the double quotes, but, for example, 'MaM' is written with double
quotes, (as ''"MaM"') in the temporary data file.

Also, I think it's generally better to remove the double quotes from
around all strings exported by org mode for plotting by gnuplot as
they're generally not needed (exceptions are strings which contain
spaces which can be quoted so they are treated as a single entity by
gnuplot).  For example, there is a gnuplot demonstration script called
datastrings.dem which plots data from a file called ctg-y2.dat.  This
data file has unquoted month names in the first column that are
plotted as labels on the x-axis.

Paul