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### 7.5 Special Tokens

There are a few pseudo-variables which have special functions in the expression language. The following specials are column-like, in that they have a different value for each row:

`$index` or `$0`
  The current row number in the underlying table (the first row is 1). This is the value seen in the grey numbers at the left of the grid in the Data Window, and is not affected by the current Row Subset or Row Order. Note that this value is a `long` (8-byte integer); when using it in certain expressions you may find it necessary to convert it to an `int` (4-byte integer) using the `toInteger()` function. The deprecated alias "`INDEX`" may also be used.
`$index0` or `$00`
  The current row number in the apparent table (the first row is 1). This value is sensitive to the current Row Subset and Row Order of the table. It has a null value for rows not in the current subset.
`$random` (Deprecated)
  A double-precision random number `0<=x<1`. NOTE: this token is deprecated since it can behave unpredictably (the same cell does not always yield the same result). Use instead the `random()` function in class Maths.

The following specials are parameter-like, in that their value is not sensitive to the row:

`$nrow`
  The number of rows in the table. This figure refers to the underlying table, not the apparent table, so it is not affected by the value of the current subset. Note that this value is a `long` (8-byte integer); when using it in certain expressions you may find it necessary to convert it to an `int` (4-byte integer) using the `toInteger()` function.
`$ncol`
  The number of columns in the table. This figure refers to the underlying table, not the apparent table, so it is not affected by hiding columns.
`$nrow0`
  The number of rows in the apparent table. This value may be less than `$nrow` if a non-default current subset is selected.
`$ncol0`
  The number of columns in the apparent table. This value will be less than `$ncol` if some columns are currently hidden.

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TOPCAT - Tool for OPerations on Catalogues And Tables
Starlink User Note253
TOPCAT web page: http://www.starlink.ac.uk/topcat/
Author email: m.b.taylor@bristol.ac.uk
Mailing list: topcat-user@jiscmail.ac.uk