获取数据框中特定分类变量的计数

Question

我有以下数据框

cars <- c("Toyota","Nissan","BMW","Nissan","Ford","Toyota","Nissan")
price <- c(21000, 23400, 26800,21000, 23400, 26800,21000)
salesDF <- data.frame(cars, price)

我想获取“Nissan”在列cars中出现的次数或次数，并将其存储在 Shiny 的 valueBox 中。我怎样才能得到那个特定的计数？在这种情况下，如何根据“Nissan”出现的次数得到值3？

Answer 1

有很多方法可以做到这一点，这里有几个：

var = 'Nissan'
#1.
value <- sum(salesDF$cars == var)
value
#[1] 3

#2.
value <- nrow(subset(salesDF, cars == var))

Answer 2

使用table to get all counts, and subset获得所需的计数：

counts <- as.data.frame(table(salesDF$cars))

print(counts)
##     Var1 Freq
## 1    BMW    1
## 2   Ford    1
## 3 Nissan    3
## 4 Toyota    2

print(subset(counts, Var1 == 'Nissan', select = -Var1))
##   Freq
## 3    3

获取数据框中特定分类变量的计数

get the count of a specific categorical variable in a data frame

r

shiny

shinydashboard