# [R] How to avoid the three loops in R?

ONKELINX, Thierry Thierry.ONKELINX at inbo.be
Fri Aug 1 15:40:19 CEST 2014

It is possible to do without loops if you start by calculating the totals. Then is just aggregating and merging data.

Best regards,

Thierry

set.seed(21)
n.country <- 5
average.price <- runif(n.country, max = 200)
price <- expand.grid(
Product = 1:10,
Country = factor(LETTERS[seq_len(n.country)]),
Year = 2000:2010
)
price\$Price <- rnorm(nrow(price), mean = average.price[price\$Country], sd = 30)
#number and sum of all prices of the product over all countries and years
total.product <- aggregate(
cbind(Price, N = 1) ~ Product,
data = price,
FUN = sum
)
#number and sum of all prices of the product per country over all years
total.product.country <- aggregate(
cbind(Pricec = Price, Nc = 1) ~ Product + Country,
data = price,
FUN = sum
)
#merge both tables
combined.price <- merge(total.product, total.product.country)
with(combined.price, Price / N) #average price
with(combined.price, Pricec / Nc) #average price per country
with(combined.price, (Price - Pricec)/ (N - Nc)) #average price in the other countries

ir. Thierry Onkelinx
Instituut voor natuur- en bosonderzoek / Research Institute for Nature and Forest
team Biometrie & Kwaliteitszorg / team Biometrics & Quality Assurance
Kliniekstraat 25
1070 Anderlecht
Belgium
+ 32 2 525 02 51
+ 32 54 43 61 85
Thierry.Onkelinx op inbo.be
www.inbo.be

To call in the statistician after the experiment is done may be no more than asking him to perform a post-mortem examination: he may be able to say what the experiment died of.
~ Sir Ronald Aylmer Fisher

The plural of anecdote is not data.
~ Roger Brinner

The combination of some data and an aching desire for an answer does not ensure that a reasonable answer can be extracted from a given body of data.
~ John Tukey

-----Oorspronkelijk bericht-----
Van: r-help-bounces op r-project.org [mailto:r-help-bounces op r-project.org] Namens PIKAL Petr
Verzonden: vrijdag 1 augustus 2014 15:18
Aan: Lingyi Ma
CC: r-help op r-project.org
Onderwerp: Re: [R] How to avoid the three loops in R?

Hi

I do not see any solution without loops but maybe others find it.

I think that you can do it in one loop. Best structure for loop will be list.

In each cycle you will compute matrix with diagonal NA

mat<-matrix(1,nrow=number of items, ncol=number of items)
diag(mat) <- NA

apply(price chunk * mat, 2, mean, na.rm=T)

So when I named your example as temp I get

fac <- interaction(factor(temp\$Product), factor(temp\$Year_Month), drop=T) lll <- split(temp, fac) for( i in 1:length(lll)) {  mat <- matrix(1,  nrow=nrow(lll[[i]]), ncol= nrow(lll[[i]]))
diag(mat) <- NA
lll[[i]]\$others <- apply(mat*lll[[i]][,3], 2, mean, na.rm=T)  }

> lll
\$`1.201204`
Country Product Price Year_Month others
1      AE       1    20     201204     24
2      DE       1    20     201204     24
3      CN       1    28     201204     20

\$`2.201204`
Country Product Price Year_Month others
4      AE       2    28     201204     25
5      DE       2    28     201204     25
6      CN       2    22     201204     28

\$`3.201204`
Country Product Price Year_Month others
7      AE       3    28     201204     28
8      CN       3    28     201204     28

\$`1.201205`
Country Product Price Year_Month others
9       AE       1    20     201205     24
10      DE       1    20     201205     24
11      CN       1    28     201205     20

\$`2.201205`
Country Product Price Year_Month others
12      AE       2    28     201205     28
13      DE       2    28     201205     28

I did not check speed but it shall be OK.

Regards
Petr

> -----Original Message-----
> From: r-help-bounces op r-project.org [mailto:r-help-bounces op r-
> project.org] On Behalf Of Lingyi Ma
> Sent: Friday, August 01, 2014 1:42 PM
> To: r-help op r-project.org
> Subject: [R] How to avoid the three loops in R?
>
> I have the following data set:
>
>   Country  Product   Price  Year_Month
>      AE         1           20    201204
>      DE         1           20    201204
>      CN         1           28    201204
>      AE         2           28    201204
>      DE         2           28    201204
>      CN         2           22    201204
>      AE         3           28    201204
>      CN         3           28    201204
>      AE         1           20    201205
>      DE         1           20    201205
>      CN         1           28    201205
>      AE         2           28    201205
>      DE         2           28    201205
>
> I want to create the one more column which is "The average price of
> the product in other areas".
> in other word, for each month, for each product, I calculate the
> average of such product in the other area.
>
> I want sth like:
>
>   Country  Product   Price  Year_Month    Price_average_In_Other_area
>      AE         1           20    201204              14
>      AE         2           28    201204              25
>
> Please avoid the three for loop, I have tried and it never end. I have
>  1070427 rows.  Is there better way to speed up my program?
>
>       [[alternative HTML version deleted]]
>
> ______________________________________________
> R-help op r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> guide.html and provide commented, minimal, self-contained,
> reproducible code.

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