Column

Column specifications may only appear in the body of a table specification. There is no limit to the number of column specifications which may appear in the table body. Within a table column names must be unique.

The general form of a column specification is given by

       column column-dimensions column-name data-type label units optional-expression 
        < 
            ... column item specifications ... 
        >

where,

• column is the column specification keyword. This keyword begins a new column specification.

• column-name is the name of the column. There must be no other column with the same name in the table. It has type string-expression (which may be a literal string).

• column-dimensions, denotes the dimensions of the column's cells.. It takes the form of a comma-separated list of integer-valued expressions, the list being delimited by parentheses. The general form is ( integer-expression, integer-expression, ... ). For instance, (10,20) indicates that the columns cells are a two dimensional matrix with size 10 by 20. See 3.1.4 for string columns. Scalar, multi-dimensional and variable length columns are supported. Scalar and multi-dimensional columns have fixed length. Variable length columns are created by setting the dimensions to 0.

• data-type specifies the data type of the column. The available types are int8, int16, int32, real32, real64, bool, string.

• label is a short textual description for the column. It has type string-expression (which may be a literal string).

• units is string containing the column's units. Its type is string-expression (which may be a literal string). When data-type is bool or string the units must be the empty string. This appears to be a limitation of CFITSIO.

• optional-expression is an optional expression which is evaluated after the last item in the body has been evaluated.

The header part of the column specification (column column-name optional-expression) must be placed onto a single line. This is due to a limitation of the parser. The subsequent body, which is delimited by and , is optional but, if present, must begin on a new line.

The column specification body comprises zero or more of the following specifications:

• attribute

The final optional expression can be used to direct deceit to execut a function. The function is executed when the interpreter reaches the end of the column specification block. The variable col is a pointer to the column and may be referenced in the expression. For example,

    dataset "set" 
    < 
       table "table" 100 
       < 
           column "col" int32 "integer column" "m" fillColumn(col, "data.dat", 0) 
        > 
    >

where fillColumn is a user-defined function (see 3.3) that takes a pointer to a column, and fills it with data from column 0 of somefile.