Hi:
On Fri, Dec 10, 2010 at 6:47 AM, Daniel Brewer <daniel.bre...@icr.ac.uk>wrote:
> Hello,
>
> I am finding that the melt function from the reshape library causes
> errors when applied to a data.frame that contains numeric and character
> columns. For example,
>
In this case, thankfully so - it's warning that you're trying to mix numeric
and factor variables.
>
> melt(id.vars="ID",data.frame(ID=1:3,date=c("a","b","c"),value=c(1,4,5)))
> ID variable value
> 1 1 date a
> 2 2 date b
> 3 3 date c
> 4 1 value <NA>
> 5 2 value <NA>
> 6 3 value <NA>
> Warning message:
> In `[<-.factor`(`*tmp*`, ri, value = c(1, 4, 5)) :
> invalid factor level, NAs generated
>
> It would be useful in this situation that the numerical column got
> converted to a character column in this situation. Any ways round this?
>
For this question, convert value to character before melting it.
>
> In actual fact I have got a situation where it is more like this
>
> ID Date_1 Value_1 Date_2 Value_2 ...
>
> and I would like to convert it to a data.frame of ID, Date & Value but I
> thought the above would be an appropriate middle step.
>
This is a more effective way, taken from a post on the ggplot2 list,
courtesy of Kohske Takahashi:
# Toy data:
df <- data.frame(id = as.character(101:110),
date1 = seq(from = as.Date('2006-01-10'),
to = as.Date('2006-01-19'), by = 'day'),
value1 = rpois(10, 5),
date2 = seq(from = as.Date('2006-02-10'),
to = as.Date('2006-02-19'), by = 'day'),
value2 = rpois(10, 10),
stringsAsFactors = FALSE)
dfm <- data.frame(
melt(df, id = 'id', measure = c(grep('^date', names(df)))),
myval = melt(df, id = 'id',
measure = c(grep('^val', names(df))))$value
)
names(dfm)[3] <- 'date'
The first melt() call creates the three variables that are normally returned
from melt(): id, variable and value. The second, internal melt() call
creates a stacked column for the values without creating a new 'variable'.
One can repeat the game with multiple sets of variables.
Of course, there is an alternative way to reshape such data with the
reshape() function...
HTH,
Dennis
Thanks
>
> Dan
> --
> **************************************************************
> Daniel Brewer, Ph.D.
>
> Institute of Cancer Research
> Molecular Carcinogenesis
> Email: daniel.bre...@icr.ac.uk
> **************************************************************
>
> The Institute of Cancer Research: Royal Cancer Hospital, a charitable
> Company Limited by Guarantee, Registered in England under Company No. 534147
> with its Registered Office at 123 Old Brompton Road, London SW7 3RP.
>
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