将自定义函数应用于r中数据框中的每一行

Question

I am trying to using each row in a data frame as inputs to a function to process some data and then write the output to a csv file. As per the following example

myfunction <- function(X, Y, Z){

                       data <- read.csv("mydata.csv")
                       subsetedData <- subset(data, x=X & y=Y & z=Z, select=x:z)
                       write.csv(subsetedData, file="mycsvfile.csv")
                       }

apply(myXYZdata, MARGIN = 1, function(x1, x2, x3) myfunction(X, Y, Z))

I want to subset based on every row in the dataframe myXYZdata. However this does not appear to work or I am not fully understanding the correct usage of apply.

I know this can be done using a loop but would prefer not to do it that way.

Edit:

The purpose of this is that I have a large data file which I want to subset based on combinations of variables found in my data frame "myXYZdata" and store the results in new data files.

The large data file I want to subset is in the format.

date                      x   y  z    count          
1 2015-08-20 00:00:00.000 a   d  h    56
2 2015-08-26 00:00:00.000 b   e  h     4
3 2015-08-18 00:00:00.000 b   f  i     8
4 2015-09-03 00:00:00.000 c   e  l     32
5 2015-08-12 00:00:00.000 a   g  l     3

Answer 1

I believe its easier to pass a row as argument to your function.

myfunction <- function(row){

                   data <- read.csv("mydata.csv")
                   subsetedData <- subset(data, x=row[1] & y=row[2] & z=row[3], select=x:z)
                   write.csv(subsetedData, file="mycsvfile.csv")
                   }

apply(myXYZdata[,c("X","Y","Z")], MARGIN = 1, myfunction)

Answer 2

What about using mapply (multi-variable apply):

mapply(myfunction, myXYZdata$X, myXYZdata$Y, myXYZdata$Z, fnms)

You will need to create a vector of file names ( fnms ) so that each entry is written to a different file and then change myfunction so that it takes an argument for the file name.

Alternatively put append = TRUE as an argument to write.csv in myfunction to get it all written to the same file (but be aware that successive runs of the code will not overwrite the file - you could precede the write.csv(..., append = TRUE) with if(file.exists("mycsvfile.csv")) file.remove("mycsvfile.csv") ).