R语言包_reshape2

names(airquality) = tolower(names(airquality))
head(airquality)

# melt
md = melt(airquality,id= c("month","day"))
md = melt(airquality,id = c("month","day"),variable.name = "climate_variable",
          value.name = "climate_value",na.rm=T)
head(md)
head(airquality)
dim(airquality)
dim(md)

# cast to data.frame
# restore original data
cd = dcast(md,month+day~climate_variable,value.var = "climate_value")
head(cd)
head(airquality)
dim(cd)
dim(airquality)
# aggregate by month to get the mean value
dcast(md,month~climate_variable,value.var = "climate_value",fun.aggregate = mean,
      na.rm=T)
# add margin
dcast(md,month~climate_variable,value.var = "climate_value",fun.aggregate = mean,
      na.rm=T, margins=c("month","climate_variable") )
# use of ...
dcast(md,month+day~...)
# use of .
dcast(md,month~.)
table(md$month)

# with plyr
library(plyr)
acast(md,climate_variable~month,mean,subset=.(climate_variable == "solar.r"))