比较数据框中某列中的元素与另一数据框中同一列中的另一个元素以获取R中的对应行

Question

I am new to programming and obviously new to R. I am learning some documents in R and started programming in R.

I have four data frames with data frame names Data1 , Data2 , Data3 , Data4 . Each data frames has eight columns ( V1 , V2 , V3 , V4 , V5 , V6 , V7 , V8 ) and 10,000 rows.The number of rows and number of columns is same for all the data frames.

I want to compare the elements of each row's 8th column ( V8 ) of all the four data frame with each other with their corresponding rows and find the maximum and minimum value. For example if I have 10 rows and 8 columns in each data frame, I have to compare the 1st row 8th column element of Data1 , Data2 , Data3 , Data4 to find the maximum and minimum value. Then i have to compare the 2nd row 8th column element of Data1 , Data2 , Data3 , Data4 to find the maximum and minimum value. Similary the 3rd row 8th column element, 4th row 8th column element and i have to do this for remaining 10,000 rows. How should I do this and what function should I use?

Answer 1

Sample data:

Data1 <- as.data.frame(matrix(runif(80), 10, 8))
Data2 <- as.data.frame(matrix(runif(80), 10, 8))
Data3 <- as.data.frame(matrix(runif(80), 10, 8))
Data4 <- as.data.frame(matrix(runif(80), 10, 8))

You can do:

pmin(Data1$V8, Data2$V8, Data3$V8, Data4$V8)
pmax(Data1$V8, Data2$V8, Data3$V8, Data4$V8)

Or something more programmatic (there can be many variations here)

Datas <- mget(paste0("Data", 1:4))
do.call(pmin, lapply(Datas, `[[`, "V8"))
do.call(pmax, lapply(Datas, `[[`, "V8"))

Answer 2

You could combine your columns in a new dataframe. Then its easy to find the row-wise min or max values:

newd <- data.frame(a=Data1$V8, b=Data2$V8, c=Data3$V8, d=Data4$V8)
apply(newd, 1, max)