Chapters:
1: Introduction
2: Simple example
3: Invocation
4: Finer Control
5: X-Y Plots
6: Contour Plots
7: Image Plots
8: Examples
9: Gri Commands
10: Programming
11: Environment
12: Emacs Mode
13: History
14: Installation
15: Gri Bugs
16: Test Suite
17: Gri in Press
18: Acknowledgments
19: License
Indices:
Concepts
Commands
Variables

### 8.12.3: Algebra on column data

Suppose the file contains (x,y), but you wish to plot 2y times x. You could do the doubling of y within Gri, as

    open file
    read columns x y
    y *= 2
    draw curve

or you could use a system tool, e.g. gawk, as in this example (see Awk).

    open "gawk '{print($1,2*$2)}' file|"
    read columns x y
    draw curve

The latter is preferable in the sense that it is more powerful. The reason for this is that Gri allows you to manipulate the x and y columns, using so-called RPN mathematics (see rpn Mathematics), but you cannot blend the columns. For example, you cannot easily form the ratio y/x in Gri. (Actually, you can, by looping through your data and doing the calculation index by index, but if you knew that already you wouldn't need to be reading this section!) Such blending is trivial in the operating system, though, as in the following Gawk example (see Awk).

    open "gawk 'print {($1, $2/$1)}' file |"
    read columns x y
    draw curve