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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
 		index.html#Top ReversePolishMath.html#rpnMathematics Gri: RPN solitary operators Gri: RPN examples index.html#Top Gri: RPN examples

10.9.7: Manipulation of Columns etc

10.9.7.1: Columns

Individual data in the `x', `y', `z', `u', `v' and `weight' columns can be accessed with the `@' operator. The first point has index 0. Examples: 


show "first x is " {rpn x 0 @ }
show "last  x is " {rpn x ..num_col_data.. 1 - @ }
show "and here are all the data:"
.i. = 0
while {rpn .i. ..num_col_data.. >}
    show {rpn x .i. @ }
    .i. += 1
end while

The mean value is available from the `mean' operator (e.g., `.xmean. = {rpn x mean }', while the standard deviation is given by `stddev', the skewness is given by `skewness', and the kurtosis is given by `kurtosis' (using the definition that yields 3 for a gaussian distribution).

The minimal and maximal values are given by `min' and `max'.

The area under the curve y=y(x) is found by `{rpn y x area }', defined by `0.5 * sum ( (y[i] + y[i-1]) * (x[i] - x[i-1]) )' for `i' ranging from 1 to `..num_col_data..'-1.

10.9.7.2: Grid

Grid data can be accessed with e.g. `{rpn grid min } ', `{rpn grid max } ', and `{rpn grid mean } '.

The value of the grid at a given `(.x.,.y.)' coordinate may be found by by e.g. `{rpn grid .x. .y. interpolate}'. The interpolation scheme is the same as that used in converting grids to images.

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