[R] R equivalent for SQL query

[jim holtman]

Here is a solution using the data.table package:

> x <- read.table(text = "A       B       C
+ 1       1       3
+ 1       1       4
+ 1       1       5
+ 1       2       6
+ 1       2       7
+ 1       3       8", header = TRUE)
> require(data.table)
> x <- data.table(x)  # convert to a data.table
> # query
> result <- x[
+           , list(count = length(C))
+           , by = list(A,B)
+           ]
> # unsorted result
> result
     A B count
[1,] 1 1     3
[2,] 1 2     2
[3,] 1 3     1
> # sorted result
> result[order(result$count, decreasing = TRUE), ]
     A B count
[1,] 1 1     3
[2,] 1 2     2
[3,] 1 3     1
>
>


On Tue, Apr 3, 2012 at 3:50 PM, andrija djurovic <djandrija at gmail.com> wrote:
> Hi,
>
> here are some solutions:
>
> DF <- read.table(textConnection("
> A       B       C
> 1       1       3
> 1       1       4
> 1       1       5
> 1       2       6
> 1       2       7
> 1       3       8 "), header=TRUE)
>
> #using sqldf package
> library(sqldf)
> sqldf("select A, B, count(*)
>      from DF
>      group by A, B
>      order by count(*) desc")
>
> #using function table
> as.data.frame(table(DF$A, DF$B))
>
> As you can see, you can use sqldf package for performing sql queries
> on R data frames.
>
> Andrija
>
>
>
> On Tue, Apr 3, 2012 at 8:26 PM, Steven Raemaekers <s.raemaekers at sig.eu> wrote:
>> Hi,
>>
>> I have a query which I would like to translate into R, but I do not know how to do it in an easy way.
>> Assume a data frame has columns A, B and C:
>>
>> A       B       C
>> 1       1       3
>> 1       1       4
>> 1       1       5
>> 1       2       6
>> 1       2       7
>> 1       3       8
>>
>> The query is as follows:
>>
>> select A, B, count(*)
>> from data.frame
>> group by A, B
>> order by count(*) desc
>>
>> How do I translate this into R statements in such way that the result is a data frame structured as follows:
>>
>> A       B       count(*)
>> 1       1       3
>> 1       2       2
>> 1       3       1
>>
>> Thanks,
>>
>> Steven
>> ______________________________________________
>> R-help at r-project.org mailing list
>> https://stat.ethz.ch/mailman/listinfo/r-help
>> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
>> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.



-- 
Jim Holtman
Data Munger Guru

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Tell me what you want to do, not how you want to do it.