R's list data structure

HI Ajay,

Given

dayOfWeekName<-c("Mon","Tue","Wed","Thu","Fri","Sat","Sun");
dayOfWeekOrdinal<-c(1,2,3,4,5,6,0);
dayOfWeekWorkDay<-c(TRUE,TRUE,TRUE,TRUE,TRUE,FALSE,FALSE);

weekProfile<-list(dow=dayOfWeekName,dowI=dayOfWeekOrdinal,dowW=dayOfWeekWorkDay)


1. How can I conditionally get dow, dowI, and dowW from weekProfile?

If another 'arrangement' of this list object will make this task easier, please advise.

2. What is the point of the list object?

I know that when mixed data types need to be held together, then the only option is to use the list data structure.

In your particular case, where all list components are the same length and are
associated with each other in order, a special type of list called a data frame
is easier to work with.

weekProfile<- data.frame(dow=dayOfWeekName,dowI=dayOfWeekOrdinal,dowW=dayOfWeekWorkDay)

weekProfile

dow dowI  dowW
1 Mon    1  TRUE
2 Tue    2  TRUE
3 Wed    3  TRUE
4 Thu    4  TRUE
5 Fri    5  TRUE
6 Sat    6 FALSE
7 Sun    0 FALSE

I'm not sure what kind of conditional you want, but this can easily be done
with subset() or [

weekProfile[weekProfile$dowW ,]

dow dowI dowW
1 Mon    1 TRUE
2 Tue    2 TRUE
3 Wed    3 TRUE
4 Thu    4 TRUE
5 Fri    5 TRUE

A regular list is excellent for holding diverse kinds of data, for example 10
lm() objects, or a series of data frames.

In a list, the third element of component 1 may not have anything whatsoever
to do with the third element of component 2.

In a data frame, rows are related.

If I were to hold recurring (Name, Salary, DateOfBirth) (i.e. character, integer and date values) in a list object, what would be the 'optimal' arrangement?

Data frame.

Would that be as the components of weekProfile above? Or will this be better.

Either:

personalDetail<- list(rbind(c(Name,Salary,DateOfBirth),c(Name,Salary,DateOfBirth)));

Sarah Goslee
http://www.functionaldiversity.org

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Hi Sarah,

??????????? Thanks you for the clarifications; I had worked round the
problem by switching to a data.frame.

??????????? However, I am still unclear about 'list': as it exists, it must
have a purpose. When is the use of the list data structure appropriate?

I gave one example: storing lm() objects.

Here's another: I'm doing a lot of spatial processing, and I read a single
multispectral image into a list. Each list component is a SpatialGridDataFrame.
That way each band from a single image is part of the same R object, and
I can use lapply() to perform an operation on each band in turn.

Using lists for things is a very Rish way of working, but it may take a
while to get the hang of it.

Sarah Goslee
http://www.functionaldiversity.org

FWIW:

Lists are a fundamental, universal, recursive data structure. All
other data structures (i.e. r.e. sets) can be represented as lists.
Indeed, one of the earliest "high level" (non-machine instructions)
computer languages, McCarthy's LISP = List Processing, is based on
lists. R was designed to be LISP-like (= a functional programming
language) in some fundamentals ways. So it is no surprise that lists
are widely used within R.

Cheers,
Bert

Hi Sarah,

??????????? Thanks you for the clarifications; I had worked round the problem by switching to a data.frame.

??????????? However, I am still unclear about 'list': as it exists, it must have a purpose. When is the use of the list data structure appropriate?

? ? ? ?[[alternative HTML version deleted]]

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