在给定另一列的值的情况下，如何计算某列中某物的实例？

Question

I basically have a data frame like this:

Name Value   
a    TRUE
a    TRUE
b    FALSE
a    FALSE
c    TRUE

but longer and I want to get the amount of times a, b, and, c appear. I also want to get the amount of time TRUE appears for a, b, and c.

So basically, I want:

Name Count TRUEs
a    3     2
b    1     0
c    1     1

How would I do that?

Answer 1

With dplyr :

library(dplyr)
df %>% group_by(Name) %>% summarise(Count = n(), Trues = sum(Value == TRUE))
# A tibble: 3 x 3
   Name Count Trues
  <chr> <int> <int>
1     a     3     2
2     b     1     0
3     c     1     1

Answer 2

A base R alternative using by

do.call(rbind, by(df, df$Name, FUN = function(x)
    c(Count = length(x$Value), TRUEs = sum(x$Value == TRUE))))
#  Count TRUEs
#a     3     2
#b     1     0
#c     1     1

Or using tapply

do.call(rbind, with(df, tapply(Value, Name, FUN = function(x)
    c(Count = length(x), TRUEs = sum(x == TRUE)))))