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RE: Manipulating List Elements In Programs

  • To: mathgroup at
  • Subject: [mg23959] RE: [mg23940] Manipulating List Elements In Programs
  • From: "David Park" <djmp at>
  • Date: Sun, 18 Jun 2000 03:00:42 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

> -----Original Message-----
> From: Buz Barstow [mailto:buz at]
To: mathgroup at
> Hi,
> I'm trying to write a program in Mathematica to automatically plot graphs
> from text files that I've generated with a C program. It looks in the
> working directory, and retrieves a list of all files with a .dat
> extension;
> files = FileNames["output*.dat"]
> Then, it gets the number of entries in that list;
> l = Length[files]
> And then uses this information to import each file individually and do a
> ListPlot with each list;
> For[i = 1, i <= l, i++,
>   z = Import[ files[[i]]];
>   title = z[[1]];
>   lab = z[[2]];
>   Delete[z, {1, 2}];
>   ListPlot[z, AxesLabel -> lab, PlotLabel -> title] ]
> At the top of each output file there is a heading that I want to
> use as the
> plot's title and two column headings that I want to use to label the axes.
> Unfortunately, I can retrieve them and label the plot, but I can't delete
> them, so when I include the title, I can't produce the plot.
> Does Mathematica prevent the programming calls deleting things, or am I
> missing something?
> Thanks in advance,
> Buz


It would be easier to use Drop.

z = {a, b, c, d};

z2 = Drop[z, 2]
{c, d}

Or, if you don't have to preserve the original z:

z = Drop[z, 2]
{c, d}

Then ListPlot z2 or the new z.

Whether you use Drop or Delete, you must do an assignment if you want the
variable to reflect the change.

David Park
djmp at

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