Description of the rate tables used by expected survival routines.

A rate table contains event rates per unit time for some particular
endpoint. Death rates are the most common use, the `survexp.us`

table, for instance, contains death rates for the United States by
year of age, sex, and calendar year.

A rate table is structured as a multi-way array with the following attributes:

- dim
the dimensions of the array

- dimnames
a named list of dimnames. The names are used to match user data to the dimensions, e.g., see the

`rmap`

argument in the`pyears`

example. If a dimension is categorical, such as`sex`

in`survexp.us`

, then the dimname itself is matched against user's data values. The matching ignored case and allows abbreviations, e.g., "M", "Male", and "male" all successfully match the`survexp.us`

dimname of`sex=c("male", "female")`

.- type
a vector giving the type of each dimension, which will be 1= categorical, 2= continuous, 3= date, 4= US calendar year. If

`type`

is 3 or 4, then the corresponding cutpoints must be one of the calendar date types: Date, POSIXt, date, or chron. This allows the code to properly match user data to the ratetable.- cutpoints
a list with one elment per dimension. If

`type=1`

then the corresponding list element should be NULL, otherwise it should be a vector of length`dim[i]`

containing the starting point of the interval to which the corresponding row/col of the array applies. Cutpoints must be in the same units as the underlying table, e.g., the`survexp.us`

table contains death rates per day, so the`age`

cutpoint vector contains age in days while`year`

contains a vector of Dates. Cutpoints do not need to be evenly spaced: the`survexp.us`

table originally had age divided up as 0-1 days, 1-7 days, 7-28 days, 28 days - 1 year, 2, 3, … 119 years. (Changes in the source of the tables made it difficult to continue splitting out the first year.)- summary
an optional summarization function. If present, it will be called with a numeric matrix that has one column per dimension and one row per observation; and the function returns a character string giving a summary of the data.

- dimid
optional attribute containing the names of the dimnames. In this case the dimnames list itself does not have names.