[R] Add columns in a dataframe and fill them from another table according to a criteria

[David Winsemius]

On Aug 1, 2009, at 9:52 AM, Meenu Sahi wrote:

> Deare R users
>
> I am new to R.
> What I want to do is explained below;-
> I have table called States.Prob which is given below:-
> This table gives the probabilities of the changes in the swap curve
> depending on the state of the swap curve. I want to put these  
> probabilities
> in my dataframe mydata(given after the prob table).
>                 Prob of States
> Changes  State1  State2 State3 State4
> a             Pa1      Pa2     Pa3     Pa4
> b             Pb1      Pb2     Pb3     Pb4
> c             Pc1      Pc2     Pc3     Pc4
> d             Pd1      Pd2     Pd3     Pd4
>
> and I have a dataframe(with 93 rows) called mydata part of which(6  
> rows) is
> given below where I want to fill in the last four columns with  
> probabilities
> taken from States.Prob according to the change and state in mydata4:-
> Change  State  PState1  PState2  PState3  PState4
> 1 b       State1  Pb1
> 2 a       State4                                           Pa4
> 3 b       State2                Pb2
> 4 c       State3                             Pc3
> 5 d       State1  Pd1
> 6 a       State3                             Pa3
>
> What I want to do is highlighted in Red.
> How can I do this easily?
>
You may have seen it in red, but we don't, ....and I, at least, cannot  
figure out what you intend.   (Per the Posting Guide, which you have  
obviously not yet read, you need to compose your question in plain old  
monochromatic text and change your mail client so it posts in plain  
text.)

If looking at the help pages for stack() and reshape() does not offer  
useful information and worked examples that meet your needs then:

An approach that would make you more populat in these parts would be  
to  make a simpler example, composed in syntactically correct R, that  
is complete in itself, and can pasted into an R session. Indicate what  
you intend as output from this simpler input.

Perhaps....

 > pstate <- read.table(textConnection("Changes  State1  State2 State3  
State4
+ a             Pa1      Pa2     Pa3     Pa4
+ b             Pb1      Pb2     Pb3     Pb4
+ c             Pc1      Pc2     Pc3     Pc4
+ d             Pd1      Pd2     Pd3     Pd4"),  header=TRUE,  
as.is=TRUE)

?stack

 > data.frame(Change=pstate[,1],
               prstate =stack(pstate[2:5])$values,
               state=stack(pstate[2:5])$ind )

#first column  is only 4 elements long, but will get recycled
# second  retreives the probabilities and may need to have  
as.numeric( ) wrapped around it if they really are numeric.
# third returns what started out as column names.

    Change prstate  state
1       a     Pa1 State1
2       b     Pb1 State1
3       c     Pc1 State1
4       d     Pd1 State1
5       a     Pa2 State2
6       b     Pb2 State2
7       c     Pc2 State2
8       d     Pd2 State2
9       a     Pa3 State3
10      b     Pb3 State3
11      c     Pc3 State3
12      d     Pd3 State3
13      a     Pa4 State4
14      b     Pb4 State4
15      c     Pc4 State4
16      d     Pd4 State4

> Many thanks for your time.
>
> kind regards
> Meenu
> P.S. Thanks for your reply John. I've tried to put only the relevant  
> columns
> of the dataframe. Hope its more clear now.
>
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David Winsemius, MD
Heritage Laboratories
West Hartford, CT