Re: [R] Running different Regressions using for loops

Rui Barradas Fri, 28 Sep 2012 04:21:41 -0700

Ok, if I'm understanding it well, you want the mean value of Price1, ,Price5? I don't know if it makes any sense, the coefficients already aremean values, but see if this is it.


price.coef <- sapply(lm.list, function(x) coef(x)[2])
mean(price.coef)


Rui Barradas
Em 28-09-2012 12:07, Krunal Nanavati escreveu:

Hi,

Yes the thing that you provided...works fine....but probably I should have
asked for some other thing.

Here is what I am trying to do....

I am trying to get the mean of Price variable....so I am entering the
below function:

          mean(names(lm.list2[[2]]$coefficient[2] ))

but this gives me an error....

        [1] NA
        Warning message:
        In mean.default(names(lm.list2[[2]]$coefficient[2])) :
        argument is not numeric or logical: returning NA

I thought by getting the text from the list variable...will help me
generate the mean for that text...which is a variable in the data...say
Price 1, Media 2....and so on

Is this a proper approach...if it is...then something more needs to be
done with the function that you provided.

If not, is there a better way...to generate the mean of a particular
variable inside the " for loop " used earlier...given below:

lm.list2 <- list()
for(i in seq_along(pricemedia)){
       regr <- paste(pricemedia[i], trendseason, sep = "+")
       fmla <- paste(response, regr, sep = "~")
       lm.list2[[i]] <- lm(as.formula(fmla), data = tryout2) }




Thanks & Regards,

Krunal Nanavati
9769-919198


-----Original Message-----
From: Rui Barradas [mailto:ruipbarra...@sapo.pt]
Sent: 28 September 2012 16:02
To: Krunal Nanavati
Cc: David Winsemius; r-help@r-project.org
Subject: Re: [R] Running different Regressions using for loops

Hello,

Try

names(lm.list2[[2]]$coefficient[2] )

Rui Barradas
Em 28-09-2012 11:29, Krunal Nanavati escreveu:

Ok...this solves a part of my problem

When I type   " lm.list2[2] " ...I get the following output

[[1]]

Call:
lm(formula = as.formula(fmla), data = tryout2)

Coefficients:
(Intercept)       Price2       Media1      Distri1        Trend
Seasonality
     13491232     -5759030        -1520        34370        48628
445351




When I enter   " lm.list2[[2]]$coefficient[2] " it gives me the below
output

Price2
-5759030

And when I enter   " lm.list2[[2]]$coefficient[[2]] " ...I get the
number...which is   -5759030


I am looking out for a way to get just the  " Price2 "....is there a
statement for that??



Thanks & Regards,

Krunal Nanavati
9769-919198


-----Original Message-----
From: Rui Barradas [mailto:ruipbarra...@sapo.pt]
Sent: 28 September 2012 15:18
To: Krunal Nanavati
Cc: David Winsemius; r-help@r-project.org
Subject: Re: [R] Running different Regressions using for loops

Hello,

To access list elements you need `[[`, like this:

summ.list[[2]]$coefficients

Or Use the extractor function,

coef(summ.list[[2]])

Rui Barradas
Em 28-09-2012 07:23, Krunal Nanavati escreveu:

Hi Rui,

Excellent!!  This is what I was looking for. Thanks for the help.

So, now I have stored the result of the 10 regressions in

"summ.list

<- lapply(lm.list2, summary)"

And now once I enter        " sum.list "....it gives me the output for

all

the 10 regressions...

I wanted to access a beta coefficient of one of the
regressions....say "Price2+Media1+Trend+Seasonality"...the result of

which is stored in"

sum.list[2] "

I entered the below statement for accessing the Beta coefficient for
Price2...

summ.list[2]$coefficients[2]

NULL

But this is giving me " NULL " as the output...

What I am looking for, is to access a beta value of a particular
variable from a particular regression output and use it for further

analysis.

Can you please help me out with this. Greatly appreciate, you guys
efforts.




Thanks & Regards,

Krunal Nanavati
9769-919198

-----Original Message-----
From: Rui Barradas [mailto:ruipbarra...@sapo.pt]
Sent: 27 September 2012 21:55
To: Krunal Nanavati
Cc: David Winsemius; r-help@r-project.org
Subject: Re: [R] Running different Regressions using for loops

Hello,

Inline.
Em 27-09-2012 13:52, Krunal Nanavati escreveu:

Hi,

Thanks for all your help. I am stuck again, but with a new problem,
on similar lines.

I have taken the problem to the next step now...i have now added 2

"for"

loops... 1 for the Price variable...and another for the Media
variable

I have taken 5 price variables...and 2 media variables with the
"trend and seasonality"(appearing in all of them)....so in all there
will be
10 regression to run now

Price 1, Media 1

Price 1, Media 2

Price 2, Media 1'

Price 2, Media 2

...and so on

I have built up a code for it...

tryout=read.table("C:\\Users\\Krunal\\Desktop\\R

tryout.csv",header=T,sep=",")

cnames <- names(tryout)
price <- cnames[grep("Price", cnames)] media <-
cnames[grep("Media", cnames)] resp <- cnames[1] regr <- cnames[7:8]
lm.list <- vector("list", 10) for(i in 1:5)

+ {
+ regress <- paste(price[i], paste(regr, collapse = "+"), sep = "+")
+ for(j in 1:2) {
+ regress1 <- paste(media[j],regress,sep="+") fmla <- paste(resp,
+ regress1, sep = "~") lm.list[[i]] <- lm(as.formula(fmla), data =
+ tryout) } }

summ.list <- lapply(lm.list, summary) summ.list



But it is only running...5 regressions...only Media 1 along with the
5 Price variables & Trend & Seasonality is regressed on
Volume...giving only
5 outputs

I feel there is something wrong with the    " lm.list[[i]] <-
lm(as.formula(fmla), data = tryout)"   statement.

No, I don't think so. If it's giving you only 5 outputs the error is
probably in the fmla construction. Put print statements to see the
results of those paste() instructions.

Supposing your data.frame is now called tryout2,


price <- paste("Price", 1:5, sep = "") media <- paste("Media", 1:2,
sep = "") pricemedia <- apply(expand.grid(price, media,
stringsAsFactors = FALSE), 1, paste, collapse="+")

response <- "Volume"
trendseason <- "Trend+Seasonality"  # do this only once

lm.list2 <- list()
for(i in seq_along(pricemedia)){
        regr <- paste(pricemedia[i], trendseason, sep = "+")
        fmla <- paste(response, regr, sep = "~")
        lm.list2[[i]] <- lm(as.formula(fmla), data = tryout2) }

The trick is to use ?expand.grid

Hope this helps,

Rui Barradas

     I am not sure about its
placement...whether it should be in loop 2 or in loop 1

Can you please help me out??










Thanks & Regards,

Krunal Nanavati
9769-919198

-----Original Message-----
From: Rui Barradas [mailto:ruipbarra...@sapo.pt]
Sent: 27 September 2012 16:22
To: David Winsemius
Cc: Krunal Nanavati; r-help@r-project.org
Subject: Re: [R] Running different Regressions using for loops

Hello,

Just to add that you can also

lapply(lm.list, coef)

with a different output.

Rui Barradas
Em 27-09-2012 09:24, David Winsemius escreveu:

On Sep 26, 2012, at 10:31 PM, Krunal Nanavati wrote:

Dear Rui,

Thanks for your time.

I have a question though, when I run the 5 regression, whose
outputs are stored in "lm.list[i]", I only get the coefficients
for the Intercept, Price, Trend & Seasonality as below

lm.list[1]

[[1]]

Call:

lm(formula = as.formula(fmla), data = tryout)

Coefficients:

(Intercept)       Price4        Trend  Seasonality

        9923123     -2606826        64616       551392

summ.list <- lapply(lm.list, summary) coef.list <-
lapply(summ.list,
coef) coef.list

I am also looking out for t stats and p value and R squared.

For the r.squared

rsq.vec <- sapply(summ.list, "$", "r.squared") adj.rsq <-
sapply(summ.list, "$", "adj.r.squared")

Do you know,
how can I get all these statistics. Also, why is " as.formula "
used in the lm function. It should work without that as well, right?

No.

Can you please tell me, why the code that I had written, does not
work with R. I thought it should work perfectly.

In R there is a difference between expression objects and character

objects.

Thanks & Regards,



Krunal Nanavati

9769-919198



*From:* Rui Barradas [mailto:ruipbarra...@sapo.pt]
*Sent:* 26 September 2012 17:13
*To:* Krunal Nanavati
*Cc:* r-help@r-project.org
*Subject:* Re: [R] Running different Regressions using for loops



Hello,

Try the following.


#cnames <- names(tryout)  # in your code, use this one cnames <-
c("Volume", "Price1", "Price2", "Price3", "Price4", "Price5",
"Trend", "Seasonaliy")

price <- cnames[grep("Price", cnames)] resp <- cnames[1] regr <-
cnames[7:8]

#lm.list <- vector("list", 5)
for(i in 1:5){
        regress <- paste(price[i], paste(regr, collapse = "+"), sep
=

"+")

        fmla <- paste(resp, regress, sep = "~")
        print(fmla)
        #lm.list[[i]] <- lm(as.formula(fmla), data = tryout) }

Hope this helps,

Rui Barradas

Em 26-09-2012 08:08, Krunal Nanavati escreveu:

Hi,


I am trying to run many different regressions using a FOR Loop.


The input data that is read into R has the following variables

.         Volume
.         Price2
.         Price3
.         Price4
.         Price5
.         Trend
.         Seasonality

I want to run 5 regressions, with the Volume as an dependent
variable and

Price, Trend & Seasonality as independent variables. I have read
the above

mentioned variables in a variable called "tryout"



I am entering the following syntax in R


for(i in 1:5)

+ {
+ result[i]=lm(Volume~Price[i]+Trend+Seasonaliy,data=tryout)
+ summary(result[i])
+ }

After running these lines.I am getting the following error message
Error in eval(expr, envir, enclos) : object 'Price' not found

Can someone help me out with this error message. Appreciate for
your time

and consideration.



      [[alternative HTML version deleted]]

David Winsemius, MD
Alameda, CA, USA


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