Section 5.3.5.3.1.2. Looped data

If the input token is a loop_ keyword, the program enters a different mode of operation. Looped data may be represented in print either as repetitive lists or in tabular format. There is no indication in a CIF dictionary of the appropriate representation (nor should there be, for what is essentially a matter of presentation) and the choice is made based on a flag associated with each data name in the map file. For non-tabular lists, the structure is translated to a sequence of codes of the form

In the case of tabulated data, the loop_ header is translated into a set of table headings and typographic codes are introduced to lay out in columnar format the values in the body of the list. The number of different data names in the loop header is counted and the data values are identified by their position in the loop modulo the total number of data names in the header (in effect, by their `phase' in the loop). In the simplest case, a command is emitted that builds a table with n columns, where n is the number of different data names. Then the data values are counted as they are processed. After every nth data value, a code is emitted indicating `end of table row' and a further code is emitted before the next value (if there is one) that means `beginning of new table row'. In all other cases, a code is emitted signifying `move to next column'.

Fig. 5.3.5.6 is a simplified extract from a table of atomic coordinates derived from the _atom_site_ loop in a CIF.

Figure 5.3.5.6 | top | pdf | markup for typesetting a table of atomic coordinates.