Create an data.frame in R with dynamically assigned column names

Question

I need to create a data.frame that will be populated one row at a time by results of a for loop. It has 45 columns: the names of five of these are static but the remainder are read in (as a vector) from an external CSV file at run time. I'm looking for something along the lines of

goalsMenu <- read.csv("Phase 1 goalsmenu.csv", header = TRUE)
colHeads <- c("analysis","patient","date",as.vector(goalsMenu$Name),"CR")
output <- data.frame(colHeads)

however this creates a one-column data.frame with column name of colHeads.

colHeads <- list("analysis","patient","date",as.vector(goalsMenu$Name),"CR")

seems a step in the right direction but I need to "flatten" it to create the desired data.frame structure

could you advise please?

Answer 1

Does this help?

goalsMenu <- paste("Name", 1:40, sep="")
output <- as.data.frame(matrix(rep(0, 5 + length(goalsMenu)), nrow=1))
names(output) <- c("analysis", "patient", "date", goalsMenu, "CR1", "CR2")

Basically, I create a data.frame output with the number of columns first and name those columns in the next step. However, be aware about mdsumner's comment! This way, all columns are of class numeric . You can deal with that later though: change the class of columns in data.frame

Answer 2

If you can fill the frame with (some) data first, then you can just assign to names(). Otherwise, you'll have to make the list first (and then later convert to data.frame):

col.names <- LETTERS[1:10]  # Example column names
data <- vector("list", length(col.names))
names(data) <- col.names
print(str(data))            # Inspect the structure

Hope this helps

Answer 3

for (k in c(1:length(names_array))) {
   #Let's make a blank column, that's the length of the data frame that I'm 
   #going to attach it to:

   temp_col<-rep(NA, nrow(my_df))

   # now here's our 2nd loop
   for(i in c(1:nrow(my_df))) {
      #process the col with some stuff
       temp_col[i] <- i
    } 

    # now we're going to attach the column to the last column in the data 
    #frame
    my_df$temp_col<-temp_col

    # now we're going to assign the name from a vector 
    # we do this by looking at the length of the names
    # array, and use that as the index
    names(my_df)[length(names(my_df))]<-names_array[k]
}