A component file (jfile) can be thought of as a boxed list stored in a file. An item of the boxed list on file is referred to as a component. The script jfiles.ijs provides the utilities for working with jfiles.
load 'jfiles'
f =. 'user\data.jf'
jcreate f
1
'first component' jappend f
0
(1.5+i.2 3) jappend f
1
('asdf';23) jappend f
2 3
(<'mum';'dad') jappend f
4
The jsize result gives file information, including the indexes of the first and last items.
jsize f 0 5 1408 0 jread f;0 +---------------+ �first component� +---------------+ jread f;1 +-----------+ �1.5 2.5 3.5� �4.5 5.5 6.5� +-----------+ jread f;2 +----+ �asdf� +----+ jread f;3 +--+ �23� +--+ jread f;4 +---------+ �+-------+� ��mum�dad�� �+-------+� +---------+ 'new' jreplace f;3 3 jread f;i.5 +----------------------------------------------+ �first component�1.5 2.5 3.5�asdf�new�+-------+� � �4.5 5.5 6.5� � ��mum�dad�� � � � � �+-------+� +----------------------------------------------+
Jfiles are documented in the J Online Documentation.