27.2 rec2csv Conversion

Record sets are not tables, even if tables can be easily emulated using records having the same fields in the same order. For example:

     a: value
     b: value
     c: value
     
     a: value
     b: value
     c: value
     
     ...

There are several ways records are more flexible than tables:

• Fields can appear in a different order in several records.
• There can be several fields with the same name in a single record.
• Records can differ in the number of fields.

Since comma-separated-values files contain tables, the rec2csv utility implements an algorithm that deals with the previous difficulties, to generate a table that is what the user expects (likewise).

The algorithm is the following. The utility first scans the specified record set, building a list with the names that will become the table header. For each field, a header is added with the form:

     FIELDNAME[_N]

where N is a number in the range 2..inf and is the “index” of the field in its containing record plus one. For example, consider the following record set:

     a: a1
     b: b11
     b: b12
     c: c1
     
     a: a2
     b: b2
     d: d2

The corresponding list of headers being:

     a b b_2 c a b d

Then duplicates are removed:

     a b b_2 c d

The resulting list of headers is then used to build the table in the generated csv file. In this case:

     "a","b","b_2","c","d"
     "a1","b11","b12","c1",
     "a2","b2",,,"d2"

Note how missing fields are implemented as empty rows in the generated csv.