如何在R中做Countifs

Question

数据：

set.seed(42)
df1 = data.frame(
  Date = seq.Date(as.Date("2018-01-01"),as.Date("2018-01-30"),1),
  value = sample(1:30),
  Y = sample(c("yes", "no"), 30, replace = TRUE)
)

df2 = data.frame(
  Date = seq.Date(as.Date("2018-01-01"),as.Date("2018-01-30"),7)
)

总之，如果数据在范围内，则可行（from my previous question）：

library(data.table)

df1$start <- df1$Date
df1$end <- df1$Date

df2$start <- df2$Date
df2$end <- df2$Date + 6

setDT(df1, key = c("start", "end"))
setDT(df2, key = c("start", "end"))

d = foverlaps(df1, df2)[, list(mySum = sum(value)), by = Date ]

我该怎么做countif？

因为当我尝试

d = foverlaps(df1, df2)[, list(mySum = count(value)), by = Date ]

我收到错误

没有适用于“group”应用于类“c”（'double'，'numeric'）的对象的方法

Answer 1

d = foverlaps(df1, df2)[, .N, by = Date]

Answer 2

我们可以使用.N：

foverlaps(df1, df2)[, list(myCount = .N), by = Date ]
#          Date myCount
# 1: 2018-01-01       7
# 2: 2018-01-08       7
# 3: 2018-01-15       7
# 4: 2018-01-22       7
# 5: 2018-01-29       2

Answer 3

如果要计算每个日期的行数，可以尝试.N

foverlaps(df1, df2)[, .(mysum = .N), by = Date ]
         Date mysum
1: 2018-01-01     7
2: 2018-01-08     7
3: 2018-01-15     7
4: 2018-01-22     7
5: 2018-01-29     2

如果您想要每个日期的唯一值计数，您可以尝试uniqueN()

foverlaps(df1, df2)[, .(mysum = uniqueN(value)), by = Date ]
         Date mysum
1: 2018-01-01     7
2: 2018-01-08     7
3: 2018-01-15     7
4: 2018-01-22     7
5: 2018-01-29     2

.N和uniqueN()都来自{data.table}。

Answer 4

而不是list(mySum = count(value))尝试c(mySum = count(value))。那么代码就是为我而运行的。

d2 <-  foverlaps(df1, df2)[, c(mySum = count(value)), by = Date ]