How to build frequency matrix in R?

问题

Suppose that the existing data frame named as A contains the following data:

Time    Var
T1      loc1
T1      loc2
T1      loc3
T2      loc2
T2      loc2
T2      loc3
T3      loc1
T3      loc3
T3      loc3

I want the output frequency matrix in R in the following format

      loc1    loc2    loc3
T1     1       1       1
T2     0       2       1
T3     1       0       2

I tried using apply(), table() but could not understand how to use them to get my required output. Can somebody suggest me some functions in R which I can use to get the required output?

回答1:

You could go for xtabs in base R

xtabs(~Time+Var, A)

#    Var
#Time loc1 loc2 loc3
#  T1    1    1    1
#  T2    0    2    1
#  T3    1    0    2

---

OR dcast from data.table

library(data.table)
dcast(A, Time~Var)

来源：https://stackoverflow.com/questions/43357603/how-to-build-frequency-matrix-in-r