R：如何根据不同的日期合并两个数据框

Question

I want to merge two dataset based on date and define specific date as different category. The first data.frame is the water quality data with the date.Shown as follows (first a few columns of the data).

Organization   ID Latitude Longitude       Date Year Month Day       Depth
1        NJHDG   19  40.6475 -74.17350 2010-06-02 2010     6   2     Surface
2        NJHDG   14  40.7919 -74.07837 2010-06-03 2010     6   3 Near Bottom
3        NJHDG    2  40.9212 -74.17550 2010-06-07 2010     6   7    Midwater
4        NJHDG    5  40.8795 -74.12066 2010-06-09 2010     6   9    Midwater
5 31ISC2RS_WQX HR8A  40.9850 -73.90833 2010-06-10 2010     6  10     Surface
6        NJHDG    6  40.8890 -74.08166 2010-06-14 2010     6  14    Midwater

Now, I have another data.frame that is a precipitation data(sample shown as follows).

    Date   PrecipitationIn
    128 2010-05-08            0.03
    129 2010-05-09            0.00
    130 2010-05-10            0.00
    131 2010-05-11            0.04
    132 2010-05-12            0.33
    133 2010-05-13            0.00

The question is that I want to define the date in the first data frame as "wet day" if the current date, previous one day, previous two day has >=0.2 inches by using the precipitation data. For example,for the date "2010-06-02" in the first data frame. If either "2010-5-31" or "2010-6-01" or"2010-6-02"has >=0.2 inches precipitation,I will define "2010-06-02" as "wet day". else, I will define "dry day". I tried to used for loop and if function to define, but I failed. Anyone has smart ideas to help me solve this problem? I really appreciate it.

Answer 1

Ok - I'm not 100% sure if I got the question correctly. Maybe this example gives you an idea how to achieve what you're looking for.

A <- read.table("path/to/your/dataset1", sep = " ", header = TRUE)
B <- read.table("path/to/your/dataset2", sep = " ", header = TRUE)

C <- merge(A, B, by = "Date")

C <- data.frame(C, day.type = NA)

for (i in 1:nrow(C)){
  if (i == 1) {
    if (C$PrecipitationIn[i] >= 0.2) {
      C$day.type[i] <- "wet day"
    } else {
      C$day.type[i] <- "dry day"
    }
  } else if (i == 2) {
    if (C$PrecipitationIn[i] >= 0.2 & C$PrecipitationIn[i-1] >= 0.2) {
      C$day.type[i] <- "wet day"
    } else {
      C$day.type[i] <- "dry day"
    }
  } else if (i > 2) {
    if (C$PrecipitationIn[i] >= 0.2 & C$PrecipitationIn[i-1] >= 0.2 & C$PrecipitationIn[i-2] >= 0.2) {
      C$day.type[i] <- "wet day"
    } else {
      C$day.type[i] <- "dry day"
    }
  } 
}