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

Joachim Audenaert Joachim.Audenaert at pcsierteelt.be
Thu Apr 16 11:36:38 CEST 2015

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 

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

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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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