Tarak Tarak - 1 year ago 156
R Question

R using dcast,melt and concatenation to reshape data frame

I have a data frame as follows:

mydf <- data.frame(Term = c('dog','cat','lion','tiger','pigeon','vulture'), Category = c('pet','pet','wild','wild','pet','wild'),
Count = c(12,14,19,7,11,10), Rate = c(0.4,0.7,0.3,0.6,0.1,0.8), Brand = c('GS','GS','MN','MN','PG','MN') )

Resulting in data frame:

Term Category Count Rate Brand
1 dog pet 12 0.4 GS
2 cat pet 14 0.7 GS
3 lion wild 19 0.3 MN
4 tiger wild 7 0.6 MN
5 pigeon pet 11 0.1 PG
6 vulture wild 10 0.8 MN

I wish to transform this data frame into following

Category pet wild
Term dog,cat,pigeon lion,tiger,vulture
Countlessthan13 dog,pigeon tiger,vulture
Ratemorethan0.5 cat tiger,vulture
Brand GS,PG MN

The row headings indicate the operations like Countlessthan13 means that Count < 13 is applied to the terms and then grouped.
Also note that brand name is unique and not reapeated.

I have tried dcast and melt...but not getting desired results.

Answer Source

We can do this using data.table. Convert the 'data.frame' to 'data.table' (setDT(mydf)), grouped by 'Category', create some summarise columns by pasteing the unique values of 'Term' where 'Count' is less than 13 or 'Rate' greater than 0.5, along with pasteing the unique elements of 'Brand'.

dt <- setDT(mydf)[, .(Term = paste(unique(Term), collapse=","),
                      Countlesstthan13 =  paste(unique(Term[Count < 13]), collapse=","),

                      Ratemorethan0.5 = paste(unique(Term[Rate > 0.5]), collapse=","), 
                      Brand = paste(unique(Brand), collapse=",")), by = Category]

From the summarised dataset ('dt'), we melt to 'long' format by specifying the 'id.var' as 'Category', then dcast it back to 'wide' format.

dcast(melt(dt, id.var = "Category", variable.name = "category"),
                            category ~Category, value.var = "value")
#           category            pet               wild
#1:             Term dog,cat,pigeon lion,tiger,vulture
#2: Countlesstthan13     dog,pigeon      tiger,vulture
#3:  Ratemorethan0.5            cat      tiger,vulture
#4:            Brand          GS,PG                 MN
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