[R] Basic help on DF creation row by row

Wed Oct 2 16:34:08 CEST 2013

Hello,

Inline.

Em 02-10-2013 15:16, rolf.kemper at renesas.com escreveu:
>
> Hello Rui,
>
> thanks a lot for the quick and exhaustive  reply !
> It shows that my understanding of DF is totally wrong.
> I'm familiar with relational DBs where the columns of table have specific data types.
> Hence , I thought a DF collum is always of one specific type and the rows are just an index equal to all columns.

Right. In a df, each column is a vector, therefore all elements are of 
the same type.
> In particular , what you call FACTORS is something new to me. I have nod idea of statistics , but looking into several examples it looks like very
> useful to me.

A factor corresponds to the statistical concept of categorical variable. 
They are internally coded as integers, with a levels attribute, giving 
the several categories of the factor.

>
> What is the best reference manual to get a better imagination of how a DF is implemented and what can I do with c() function ?
> The doc I found so-far is not very exhaustive.

Try the R project home page, http://www.r-project.org. There's a link to 
several manuals, on the lower left.

Rui Barradas
>
> Thanks a lot
> R. Kemper
>
>
>
>
>
>
> Rolf  Kemper, Manager, Mixed Signal Design, Networking, Renesas Electronics Europe GmbH, , Arcadiastr. 10, 40472, Duesseldorf, Germany,  Phone:+49 211
> 6503-1475, Fax:+49 211 6503-1540, mailto:Rolf.Kemper at renesas.com, http://www.renesas.eu
>
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> From:	Rui Barradas <ruipbarradas at sapo.pt>
> To:	rolf.kemper at renesas.com,
> Cc:	r-help at r-project.org
> Date:	10/01/2013 08:38 PM
> Subject:	Re: [R] Basic help on  DF creation row by row
>
>
>
> Hello,
>
> The main problem is in the way you form newRow. You can't mix data
> classes in a vector created with c(), so all its elements become
> characters, the least common denominator:
>
> newRow <- c("primitiveSpace", 1.1 , "mm2")
> newRow
> [1] "primitiveSpace" "1.1"            "mm2"
>
>
> Then when you rbind it with the data frame, they are all converted to
> factors. This is because the default behavior is to have the option
> stringsAsFactors set to TRUE. Try to check it:
>
> options()$stringsAsFactors  # TRUE
>
>
> Now, each of those factors was created with only one level, so when you
> try to assign something different to them, with the second rbind, NAs
> are generated.
>
> The correct way would be something like the following.
>
>
> newRow <- data.frame(item = "primitiveSpace", value = 1.1 , unit = "mm2")
> deviceSummary <- rbind(deviceSummary , newRow )
> print(deviceSummary)
> str(deviceSummary)  # to check what you have
>
> newRow <- data.frame(item = "primitiveCellSpace", value = 2.2 , unit =
> "mm2")
> deviceSummary <-rbind(deviceSummary , newRow )
> print(deviceSummary )
>
>
> Hope this helps,
>
> Rui Barradas
>
> Em 01-10-2013 14:24, rolf.kemper at renesas.com escreveu:
>>
>>
>> Dear Experts
>>
>> I'm very new to R and after some days or reading and testing  I tried to make my first small application (and failed ...)
>> In general I would like to work with sqldf , ggplot2 to create some graphical output.
>>
>> At present I got stuck with this:
>>
>> PROG #############################################################################
>> deviceSummary <- data.frame(item = character(0) ,  value = numeric(0) , unit = character(0) )
>> print ( sapply(deviceSummary, class))
>>
>> newRow <- c("primitiveSpace", 1.1 , "mm2")
>> deviceSummary <-rbind(deviceSummary , newRow )
>> print(deviceSummary)
>>
>> newRow <- c("primitiveCellSpace", 2.2 , "mm2")
>> deviceSummary <-rbind(deviceSummary , newRow )
>> print(deviceSummary )
>>
>> OUTPUT ############################################################################
>>       item     value      unit
>>    "factor" "numeric"  "factor"
>>     X.primitiveSpace. X.1.1. X.mm2.
>> 1    primitiveSpace    1.1    mm2
>>     X.primitiveSpace. X.1.1. X.mm2.
>> 1    primitiveSpace    1.1    mm2
>> 2              <NA>   <NA>    mm2
>> Warning messages:
>> 1: In `[<-.factor`(`*tmp*`, ri, value = "primitiveCellSpace") :
>>     invalid factor level, NA generated
>> 2: In `[<-.factor`(`*tmp*`, ri, value = "2.2") :
>>     invalid factor level, NA generated
>>
>> Inserting the first record went fine , but the next one will fail as you can see.
>> Repeating only the first one (value1.1) went fine.
>>
>> May be my imagination of DF is totally wrong. Hope someone can guide me.
>>
>> Thanks a lot
>>
>> Rolf
>>
>>
>>
>>
>> Rolf  Kemper, Manager, Mixed Signal Design, Networking, Renesas Electronics Europe GmbH, , Arcadiastr. 10, 40472, Duesseldorf, Germany,  Phone:+49
> 211
>> 6503-1475, Fax:+49 211 6503-1540, mailto:Rolf.Kemper at renesas.com, http://www.renesas.eu
>>
>> This message is intended only for the use of the address...{{dropped:24}}
>>
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>