计算与基于级别因子的限制相关联的行数，该限制取决于另一个变量的最大值

Question

Sorry for the vague title but I did not know how to describe it shortly. I am working dataframe with many variables.

Basically, two variables interest me : one is a factor vector with two levels (example green, red) the other one this a numerical continuous vector (example : concentration of pesticides)

   AppleColour PesticidesConcentration
1        green                    1.45
2          red                    3.50
3        green                    1.56
4          red                   54.30
5          red                   53.20
6          red                   53.40
7        green                    2.50
8        green                    6.70
9          red                   32.05
10       green                   34.27

I wanna count the number of green 1) when pesticides >4 but <50, 2) when pesticides >20.

df1 <- structure(list(AppleColour = structure(c(1L, 2L, 1L, 2L, 2L, 
2L, 1L, 1L, 2L, 1L), .Label = c("green", "red"), class = "factor"), 
    PesticidesConcentration = c(1.45, 3.5, 1.56, 54.3, 53.2, 
    53.4, 2.5, 6.7, 32.05, 34.27)), .Names = c("AppleColour", 
"PesticidesConcentration"), class = "data.frame", row.names = c("1", 
"2", "3", "4", "5", "6", "7", "8", "9", "10"))

Answer 1

We can create logical vector with == , & , > , < and get the sum of TRUE values.

with(df1, sum(AppleColour=="green" &
    PesticidesConcentration > 4 & PesticidesConcentration <50 &
             !is.na(PesticidesConcentration)))

with(df1, sum(AppleColour == "green" &
        PesticidesConcentration  > 20 & 
        !is.na(PesticidesConcentration)))