Aggregate and reshape from long to wide
Your data are already in a long format that can be used easily by "reshape2", like this:
library(reshape)
dcast(df, bdate ~ sex + age + diag, value.var = "admissions")
# bdate Female_35-64_card Female_35-64_cere Female_65-74_card Female_65-74_cere
# 1 1987-01-01 1 6 1 6
# 2 1987-01-02 4 4 0 6
# 3 1987-01-03 2 6 4 5
# Male_35-64_card Male_35-64_cere Male_65-74_card Male_65-74_cere
# 1 0 6 0 1
# 2 0 5 0 2
# 3 1 6 0 4
I don't see any aggregation in your sample output, but if aggregation is required, you can achieve this with the fun.aggregate
function within dcast
.