[R] Assoociative array?
Duncan Murdoch
murdoch at stats.uwo.ca
Sat Jul 12 18:52:05 CEST 2008
On 12/07/2008 12:31 PM, rkevinburton at charter.net wrote:
> I am using a simple R statement to read in the file:
>
> a <- read.csv("Sample.dat", header=TRUE)
>
> There is alot of data but the first few lines look like:
>
> DayOfYear,Quantity,Fraction,Category,SubCategory
> 1,82,0.0000390392720794458,(Unknown),(Unknown)
> 2,78,0.0000371349173438631,(Unknown),(Unknown)
> . . .
> 71,2,0.0000009521773677913,WOMEN,Piratesses
> 72,4,0.0000019043547355827,WOMEN,Piratesses
> 73,3,0.0000014282660516870,WOMEN,Piratesses
> 74,14,0.0000066652415745395,WOMEN,Piratesses
> 75,2,0.0000009521773677913,WOMEN,Piratesses
>
> If I read the data in as above, the command
>
> a[1]
>
> results in the output
>
> [ reached getOption("max.print") -- omitted 16193 rows ]]
>
> Shouldn't this be the first row?
No, the first row would be a[1,]. read.csv() returns a dataframe, and
those are indexed with two indices to treat them like a matrix, or with
one index to treat them like a list of their columns.
Duncan Murdoch
>
> a$Category[1]
>
> results in the output
>
> [1] (Unknown)
> 4464 Levels: Tags ... WOMEN
>
> But
>
> a$Category[365]
>
> gives me:
>
> [1] 7 Plates (Dessert),Western\n120,5,0.0000023804434194784,7 Plates (Dessert)
> 4464 Levels: Tags ... WOMEN
>
> There is something fundamental about either vectors of the read.csv command that I am missing here.
>
> Thank you.
>
> Kevin
>
> ---- jim holtman <jholtman at gmail.com> wrote:
>> Please provide commented, minimal, self-contained, reproducible code,
>> or at least a before/after of what you data would look like. Taking a
>> guess at what you are asking, here is one way of doing it:
>>
>>
>>> x <- data.frame(cat=sample(LETTERS[1:3],20,TRUE),a=1:20, b=runif(20))
>>> x
>> cat a b
>> 1 B 1 0.65472393
>> 2 C 2 0.35319727
>> 3 B 3 0.27026015
>> 4 A 4 0.99268406
>> 5 C 5 0.63349326
>> 6 A 6 0.21320814
>> 7 C 7 0.12937235
>> 8 A 8 0.47811803
>> 9 A 9 0.92407447
>> 10 A 10 0.59876097
>> 11 A 11 0.97617069
>> 12 A 12 0.73179251
>> 13 B 13 0.35672691
>> 14 C 14 0.43147369
>> 15 C 15 0.14821156
>> 16 C 16 0.01307758
>> 17 B 17 0.71556607
>> 18 B 18 0.10318424
>> 19 C 19 0.44628435
>> 20 B 20 0.64010105
>>> # create a list of the indices of the data grouped by 'cat'
>>> split(seq(nrow(x)), x$cat)
>> $A
>> [1] 4 6 8 9 10 11 12
>>
>> $B
>> [1] 1 3 13 17 18 20
>>
>> $C
>> [1] 2 5 7 14 15 16 19
>>
>>> # or do you want the data
>>> split(x, x$cat)
>> $A
>> cat a b
>> 4 A 4 0.9926841
>> 6 A 6 0.2132081
>> 8 A 8 0.4781180
>> 9 A 9 0.9240745
>> 10 A 10 0.5987610
>> 11 A 11 0.9761707
>> 12 A 12 0.7317925
>>
>> $B
>> cat a b
>> 1 B 1 0.6547239
>> 3 B 3 0.2702601
>> 13 B 13 0.3567269
>> 17 B 17 0.7155661
>> 18 B 18 0.1031842
>> 20 B 20 0.6401010
>>
>> $C
>> cat a b
>> 2 C 2 0.35319727
>> 5 C 5 0.63349326
>> 7 C 7 0.12937235
>> 14 C 14 0.43147369
>> 15 C 15 0.14821156
>> 16 C 16 0.01307758
>> 19 C 19 0.44628435
>>
>>
>> On Sat, Jul 12, 2008 at 3:32 AM, <rkevinburton at charter.net> wrote:
>>> I have search the archive and I could not find what I need so I will try to ask the question here.
>>>
>>> I read a table in (read.table)
>>>
>>> a <- read.table(.....)
>>>
>>> The table has column names like DayOfYear, Quantity, and Category.
>>>
>>> The values in the row for Category are strings (characters).
>>>
>>> I want to get all of the rows grouped by Category. The number of unique category names could be around 50. Say for argument sake the number of categories is exactly 50. Can I somehow get a vector of length 50 containing the rows corresponding to the category (another vector)? I realize I can access any row a[i]$Category (right?). But I wanta vector containing the rows corresponding to each distinct Category name.
>>>
>>> Thank you.
>>>
>>> Kevin
>>>
>>> ______________________________________________
>>> 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
>> Cincinnati, OH
>> +1 513 646 9390
>>
>> What is the problem you are trying to solve?
>
> ______________________________________________
> 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.
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