3.5.5 ASCII

In many cases tables are stored in some sort of unstructured plain text format, with cells separated by spaces or some other delimiters. The AsciiTableBuilder class attempts to read these and interpret what's there in sensible ways, but since there are so many possibilities of different delimiters and formats for exactly how values are specified, it won't always succeed.

Here are the rules for how the ASCII-format table handler reads tables:

• Bytes in the file are interpreted as ASCII characters
• Each table row is represented by a single line of text
• Lines are terminated by one or more contiguous line termination characters: line feed (0x0A) or carriage return (0x0D)
• Within a line, fields are separated by one or more whitespace characters: space (" ") or tab (0x09)
• A field is either an unquoted sequence of non-whitespace characters, or a sequence of non-newline characters between matching single (') or double (") quote characters - spaces are therefore allowed in quoted fields
• Within a quoted field, whitespace characters are permitted and are treated literally
• Within a quoted field, any character preceded by a backslash character ("\") is treated literally. This allows quote characters to appear within a quoted string.
• An empty quoted string (two adjacent quotes) or the string "null (unquoted) represents the null value
• All data lines must contain the same number of fields (this is the number of columns in the table)
• The data type of a column is guessed according to the fields that appear in the table. If all the fields in one column can be parsed as integers (or null values), then that column will turn into an integer-type column. The types that are tried, in order of preference, are: Boolean, Short Integer, Long, Float, Double, String
• Empty lines are ignored
• Anything after a hash character "#" (except one in a quoted string) on a line is ignored as far as table data goes; any line which starts with a "!" is also ignored. However, lines which start with a "#" or "!" at the start of the table (before any data lines) will be interpreted as metadata as follows:
  • The last "#"/"!"-starting line before the first data line may contain the column names. If it has the same number of fields as there are columns in the table, each field will be taken to be the title of the corresponding column. Otherwise, it will be taken as a normal comment line.
  • Any comment lines before the first data line not covered by the above will be concatenated to form the "description" parameter of the table.

If the list of rules above looks frightening, don't worry, in many cases it ought to make sense of a table without you having to read the small print. Here is an example of a suitable ASCII-format table:

    #
    # Here is a list of some animals.
    #
    # RECNO  SPECIES         NAME         LEGS   HEIGHT/m
      1      pig             "Pigling Bland"  4  0.8
      2      cow             Daisy        4      2
      3      goldfish        Dobbin       ""     0.05
      4      ant             ""           6      0.001
      5      ant             ""           6      0.001
      6      ant             ''           6      0.001
      7      "queen ant"     'Ma\'am'     6      2e-3
      8      human           "Mark"       2      1.8

    Name       Type
    ----       ----
    RECNO      Integer
    SPECIES    String
    NAME       String
    LEGS       Integer
    HEIGHT/m   Float

If you understand the format of your files but they don't exactly match the criteria above, the best thing is probably to write a simple free-standing program or script which will convert them into the format described here. You may find Perl, awk or sed suitable languages for this sort of thing. Alternatively, you could write a new input handler as explained in Section 3.1 - you may find it easiest to subclass the uk.ac.starlink.table.formats.StreamStarTable class in this case.