date.object {survival} | R Documentation

## Date Objects

### Description

Objects of class `"date"`.

### Usage

    is.date(x)

### Arguments

`x` | any R object.

### Details

Dates are stored as the number of days since 1/1/1960, and are kept in integer format. (This is the same baseline value as is used by SAS). The numerical methods for dates treat `date - date` as a numeric, and `date +- numeric` as a date.

`is.date` returns `TRUE` if `x` has class `"date"`, and `FALSE` otherwise. Its behavior is unaffected by any attributes of `x`; for example, `x` could be a date array (in contrast to the behavior of `is.vector`).

`as.date` returns `x` if `x` is a simple object of class `"date"`, and otherwise a date vector of the same length as `x` and with data resulting from coercing the elements of `x` to class `"date"`. See the manual page for `as.date()` for details.

Logical operations as well as the numeric functions `exp()`, `log()`, and so on are invalid.

Other methods exist for missing value, `as.character()`, printing, and summarizing.

### See Also

`date.mdy`, `mdy.date`, `date.ddmmmyy`, `as.date`.

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