R数据框列名称重命名

Question

I am new to R and not sure why I have to rename data frame column names at the end of the program though I have defined data frame with column names at the beginning of the program. The use of the data frame is, I got two columns where I have to save sequence under ID column and some sort of number in NOBS column.

complete <- function(directory, id = 1:332) {

  collectCounts = data.frame(id=numeric(), nobs=numeric()) 

  for(i in id)  {
    fileName = sprintf("%03d",i)
    fileLocation = paste(directory, "/", fileName,".csv", sep="")

    fileData = read.csv(fileLocation, header=TRUE)
    completeCount = sum(!is.na(fileData[,2]), na.rm=TRUE)

    collectCounts <- rbind(collectCounts, c(id=i, completeCount))
    #print(completeCount)

  }

  colnames(collectCounts)[1] <- "id"
  colnames(collectCounts)[2] <- "nobs"  
  print(collectCounts)  

}

Answer 1

Its not quite clear what your specific problem is, as you did not provide a complete and verifiable example . But I can give a few pointers on improving the code, nonetheless.

1) It is not recommended to 'grow' a data.frame within a loop. This is extremely inefficient in R, as it copies the entire structure each time. Better is to assign the whole data.frame at the outset, then fill in the rows in the loop.

2) R has a handy function paste0 that does not require you to specify sep = "" .

3) There's no need to specify na.rm = TRUE in your sum , because is.na will never return NA's

Putting this together:

complete = function(directory, id = 1:332) {
  collectCounts = data.frame(id=id, nobs=numeric(length(id))) 
  for(i in 1:length(id))  {
    fileName = sprintf("%03d", id[i])
    fileLocation = paste0(directory, "/", fileName,".csv")
    fileData = read.csv(fileLocation, header=TRUE)
    completeCount = sum(!is.na(fileData[, 2]))
    collectCounts[i, 'nobs'] <- completeCount
  }
}

Answer 2

Always hard to answer questions without example data.

You could start with

collectCounts = data.frame(id, nobs=NA)

And in your loop, do:

collectCounts[i, 2] <- completeCount

Here is another way to do this:

complete <- function(directory, id = 1:332) {
    nobs <- sapply(id, function(i) {
            fileName = paste0(sprintf("%03d",i), ".csv")
            fileLocation = file.path(directory, fileName)
            fileData = read.csv(fileLocation, header=TRUE)
            sum(!is.na(fileData[,2]), na.rm=TRUE)
        }
    )
    data.frame(id=id, nobs=nobs)
}