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One of the kool things about R is if I type the function name I get to see the implementation. But this one is confusing me, recursively:
> library(xts) > align.time function (x, ...) { UseMethod("align.time") } <environment: namespace:xts> x is an XTS object, so doesn't that mean it will call the XTS align.time method... but that is what I'm looking at! (Typing xts::align.time gives exactly the same response.)
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(See also the draft 'R Language Definition'.) UseMethod creates a new function call with arguments matched as they came in to the generic. Any local variables defined before the call to UseMethod are retained (unlike S). Any statements after the call to UseMethod will not be evaluated as UseMethod does not return.
An S3 class is the most prevalent and used class in R programming. It is easy to implement this class and most of the predefined classes are of this type. An S3 object is basically a list with its class attributes assigned some names. And the member variable of the object created is the components of the list.
S3 refers to a class system built into R. The system governs how R handles objects of different classes. Certain R functions will look up an object's S3 class, and then behave differently in response. The print function is like this.
R possesses a simple generic function mechanism which can be used for an object-oriented style of programming. Method dispatch takes place based on the class(es) of the first argument to the generic function or of the object supplied as an argument to UseMethod or NextMethod .
The short answer is that you are looking for the function xts:::align.time.xts.
The longer answer is that you can find which methods exist for align.time by calling methods:
> methods(align.time) [1] align.time.POSIXct* align.time.POSIXlt* align.time.xts* Non-visible functions are asterisked This tells you that there is a method align.time.xts that is not exported from the namespace. At this point you can probably guess that it can be found in package xts, but you can confirm that with getAnywhere:
> getAnywhere("align.time.xts") A single object matching 'align.time.xts' was found It was found in the following places registered S3 method for align.time from namespace xts namespace:xts with value function (x, n = 60, ...) { if (n <= 0) stop("'n' must be positive") .xts(x, .index(x) + (n - .index(x)%%n), tzone = indexTZ(x), tclass = indexClass(x)) } <environment: namespace:xts> You can, of course, read the source directly, but since the function is not exported, you need to use package:::function (i.e. three colons):
> xts:::align.time.xts function (x, n = 60, ...) { if (n <= 0) stop("'n' must be positive") .xts(x, .index(x) + (n - .index(x)%%n), tzone = indexTZ(x), tclass = indexClass(x)) } <environment: namespace:xts> align.time() is exported from the xts namespace, so xts::align.time and align.time are the same thing. You need to note that there is an align.time() method for objects of class "xts" provided in the package and that is not exported from the namespace (it is just registered as an S3 method):
> xts:::align.time.xts function (x, n = 60, ...) { if (n <= 0) stop("'n' must be positive") .xts(x, .index(x) + (n - .index(x)%%n), tzone = indexTZ(x), tclass = indexClass(x)) } <environment: namespace:xts> It is this method that is being called when you pass an "xts" object to align.time().
When you call align.time() UseMethod() sets up the search for and call of the appropriate "align.time" method, if available, for the class of object supplied as the first argument. UseMethod is doing exactly what you think it is doing, you have just confused yourself by looking at the same function (the generic) in two different ways.
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