[R] melt function chooses wrong id variable with large datasets

PIKAL Petr petr.pikal at precheza.cz
Thu Apr 16 12:13:20 CEST 2015


Hi

There is something weird with your data and melt function.

AFAIK melt does not use first row as id.variables.

What is result of

str(dataset)

Instead of

melt(dataset,id.vars=dataset[1,], na.rm=TRUE)

melt expects something like

melt(dataset, id.vars=c("norm, "jaar"), na.rm=TRUE)

If you want more specific answer you shall show us part of your data, preferably copy output of

dput(dataset[1:20,])

into your mail.

Cheers
Petr

> -----Original Message-----
> From: R-help [mailto:r-help-bounces at r-project.org] On Behalf Of Joachim
> Audenaert
> Sent: Thursday, April 16, 2015 11:37 AM
> To: r-help at r-project.org
> Subject: [R] melt function chooses wrong id variable with large
> datasets
>
> Hello all,
>
> I'm using a large dataset consisting of 2 groups of data, 2 columns in
> excel with a header (group name) and 15 000 rows of data. I would like
> like to compare this data, so I transform my dataset with the melt
> function to get 1 column of data and 1 column of ID variables, then I
> can apply different statistical tests. With small datasets this works
> great, the melt function automatically chooses the name in row 1 as ID
> variable and melts the data, thus giving me a matrix with all ID
> variables in column one and the data accordingly in column 2.
> With this big dataset however it chooses the whole first column as ID
> variables in stead of the first row. Is there a reason why this happens
> and how can I make sure the first row is chosen as ID variabele and the
> lower rows as data?
>
> If I specify that I want the first row to be the id variable I also get
> error.
>
> melt(dataset,id.vars=dataset[1,], na.rm=TRUE)
>
> Error: id variables not found in data: norm, jaar
>
> Are there alternative ways to create a good reshaped dataset?
>
> Met vriendelijke groeten - With kind regards,
>
> Joachim Audenaert
> onderzoeker gewasbescherming - crop protection researcher
>
> PCS | proefcentrum voor sierteelt - ornamental plant research
>
> Schaessestraat 18, 9070 Destelbergen, Belgi
> T: +32 (0)9 353 94 71 | F: +32 (0)9 353 94 95
> E: joachim.audenaert at pcsierteelt.be | W: www.pcsierteelt.be
>
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