Interfaces/R/Rserver/Formats/SEXP
Calls to R return one of:
- an integer
- a character string
- a SEXP expression
SEXP is the internal format used by R objects, and is used in most cases. It is defined in Rinternals.h.
A SEXP expression is either data, or an attribute;data pair:
- data is a list without attributes.
- attribute is a list of value;tag pairs, where the tag is an R internal name, such as class.
The data items and tag values may themselves be SEXP expressions.
In J, in order to distinguish an attribute;data pair from a data item that is a 2-element list, the attribute;data pair is given as a 1x2 matrix. This suffices, since any other data item must be a singleton or a list.
In J also, the tag names are prefixed with (backtick).
Example 1
In this example, the data is the list 2 4 3 1. The attribute class has value factor, and the attribute levels has value ;:'four one three two'.
Rgetexp 'x=factor(c("one","two","three","four"))'
┌────────────────────────────────────────────┬───────┐
│┌────────────────────┬───────┬──────┬──────┐│2 4 3 1│
││┌────┬───┬─────┬───┐│`levels│factor│`class││ │
│││four│one│three│two││ │ │ ││ │
││└────┴───┴─────┴───┘│ │ │ ││ │
│└────────────────────┴───────┴──────┴──────┘│ │
└────────────────────────────────────────────┴───────┘
Example 2
An array is represented as a data list, with the dim attribute:
Rgetexp 'array(1:6,c(2,3,4))' ┌────────────┬───────────────────────────────────────────────┐ │┌─────┬────┐│1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6 1 2 3 4 5 6│ ││2 3 4│`dim││ │ │└─────┴────┘│ │ └────────────┴───────────────────────────────────────────────┘
Example 3
The names attribute has names for the data items:
'x' Rset 12 18 24 30 36 42 48 'y' Rset 5.27 5.68 6.25 7.21 8.02 8.71 8.42 'att data'=. ,Rgetexp 'lsfit(x,y)' att ┌─────────────────────────────────────┬──────┐ │┌────────────┬─────────┬─────────┬──┐│`names│ ││coefficients│residuals│intercept│qr││ │ │└────────────┴─────────┴─────────┴──┘│ │ └─────────────────────────────────────┴──────┘ $data 4
The items in data may themselves be SEXP expressions:
0 pick data ┌──────────────────────┬────────────────┐ │┌─────────────┬──────┐│3.99429 0.102857│ ││┌─────────┬─┐│`names││ │ │││Intercept│X││ ││ │ ││└─────────┴─┘│ ││ │ │└─────────────┴──────┘│ │ └──────────────────────┴────────────────┘ 1 pick data 0.0414286 _0.165714 _0.212857 0.13 0.322857 0.395714 _0.511429 2 pick data 1 3 pick data ┌───────────────────────────────────────────────┬───────────────────────────────────────────────────... │┌────────────────────────────┬──────┬──┬──────┐│┌──────────────────────────────────────────────────... ││┌──┬──┬─────┬────┬─────┬───┐│`names│qr│`class│││_18.7319 3.26561 _0.219372 0.0961104 0.261593 0.30... │││qt│qr│qraux│rank│pivot│tol││ │ │ │││ ... ││└──┴──┴─────┴────┴─────┴───┘│ │ │ │││ ... │└────────────────────────────┴──────┴──┴──────┘││ ... │ ││ ... │ ││ ... │ ││ ... │ ││ ... │ ││ ... │ │└──────────────────────────────────────────────────... └───────────────────────────────────────────────┴───────────────────────────────────────────────────...