在 R 中读取并转换为数据帧

Question

I just imported a csv file as a data frame. I did this.

myframe <- data.frame(read.csv("afile.csv"))

but when I use the 'typeof()' function on 'myframe', I get a list.

> typeof(myframe)
[1] "list"

'myframe' turns out to be a nested list. Trying to change the name of the 9th list in the myframe does absolutely nothing. I don't even get an error. This is my code.

colnames(myframe[9]) <- "ColName"

I am not able to convert this list to a data frame either (No matter what I do). Any method I try throws up no errors and yet does nothing. I tried this.

myframe <- as.data.frame(myframe)

and

myframe  <-  as.data.frame(matrix(unlist(myframe), nrow=length(unlist(myframe[1]))))

(as suggested on a different post)

So this is basically a 4 part question,

1. Is my R behaving as expected?
2. Why isn't an error being returned?
3. How can change the name of that column?
4. How do I convert the nested list to a data frame?

Answer 1

There are couple of issues in the OP's post.

1. Reading as a data.frame

   The read.csv gives a data.frame output. So, there is no need to wrap with data.frame ie

   myframe <- read.csv("afile.csv")

   If the delimiter is different, use the sep argument and also for non-numeric variables, the default option (because stringsAsFactors=TRUE ) for read.csv will be to return the class as factor . In that case, use stringsAsFactors=FALSE .

2. Changing the column names in the dataset. This can be done by selecting the column names that we want to change. As we are changing the 9th column name, select that by indexing and then assign ( <- ) it to new name.

    colnames(myframe)[9] <- "ColName"

3. By checking the typeof(myframe) , it will give "list" as data.frame is a list with length of the list elements equal. If we want to check whether it is a data.frame

    is.data.frame(myfile)

   or

   str(myframe)

4. Error message are returned only when there is an error . Here, it won't give an error as you are wrapping a data.frame by a data.frame call. For example

   df1 <- data.frame(v1 = 1:5) str(df1) #'data.frame': 5 obs. of 1 variable: #$ v1: int 1 2 3 4 5

   Wrapping with data.frame is not going to change anything except that it is redundant. Of course, we can do data.frame(data.frame(data.frame(df1))) to test as an exercise.

    str(data.frame(df1)) #'data.frame': 5 obs. of 1 variable: #$ v1: int 1 2 3 4 5

Answer 2

The default storing of file is a dataframe. No need to make it a dataframe.

    myframe <- read.csv(file.choose(),sep=",",header=T) #Select your file interactively.
    class(myframe)       
    mode(myframe)
    typeof(myframe)
    names(myframe)[9] <- "ColName"   ## Renaming column no. 9 of dataframe