comparing an element in a column in a data frame with another element in the same column in another data frame for corresponding rows in R

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)