按列汇总字符矩阵

Question

我对R很新，所以我确信有一个简单的方法可以做到这一点，但没有太多运气。

我有一个在运行时具有未知列数和行数的矩阵。如何返回具有匹配数据的行的计数次数？

如果我有矩阵m：

names <- c("John","Bob","John","Sarah","Jill","Sarah","John")
ages <- c("25","36","25","30","55","30","55")
home <- c("USA","Canada","USA","Canada","USA","Canada","Mexico")

m <- data.matrix(cbind(names,ages,home))

如何以此格式返回数据？

+-------+------+--------+-------+
| names | ages |  home  | count |
+-------+------+--------+-------+
| John  |   25 | USA    |     2 |
| Bob   |   36 | Canada |     1 |
| Sarah |   30 | Canada |     2 |
| Jill  |   55 | USA    |     1 |
| John  |   55 | Mexico |     1 |
+-------+------+--------+-------+

Answer 1

你可以这样做：

library(data.table)
data.table(m)[,list(count=.N),by=list(names, ages, home)]

#        names ages   home count
#1:  John   25    USA     2
#2:   Bob   36 Canada     1
#3: Sarah   30 Canada     2
#4:  Jill   55    USA     1
#5:  John   55 Mexico     1