#    am     qsec        vs am     gear     carb
# 1:  1 17.36000 0.5384615  1 4.384615 2.923077
# 2:  1 17.02000 1.0000000  1 4.000000 2.000000
# 3:  0 18.18316 0.3684211  0 3.210526 2.736842
# 4:  0 17.82000 0.0000000  0 3.000000 3.000000

#    variable          0          1
 # 1:     qsec 18.1831579 17.3600000
 # 2:     qsec 17.8200000 17.0200000
 # 3:       vs  0.3684211  0.5384615
 # 4:       vs  0.0000000  1.0000000
 # 5:       am  0.0000000  1.0000000
 # <snip>

library(data.table)
data = setDT(mtcars[7:11])

# data in
tdat = data[, lapply(.SD, function(y){
                      unlist(lapply(c(mean, median), function(f) f(y) ))
                   }),
                  by="am", .SDcols=seq_along(data)
              ]


# data out
m = melt(tdat, id.vars="am")
m[, r:=duplicated(interaction(am, variable))+0L]
dcast(m, variable + r ~ am, value.var = "value")[, r:=NULL][]

dcast( melt(tdat, id.var=1), variable~am, value.var='value')
#Aggregate function missing, defaulting to 'length'
#   variable 0 1
#1:     qsec 2 2
#2:       vs 2 2
#3:       am 2 2
#4:     gear 2 2
#5:     carb 2 2