R define dimensions of empty data frame

Question

I am trying to collect some data from multiple subsets of a data set and need to create a data frame to collect the results. My problem is don\'t know how to create an empt

Answer 1

You may use NULL instead of NA. This creates a truly empty data frame.

Answer 2

df = data.frame(matrix("", ncol = 3, nrow = 10)  

Answer 3

If only the column names are available like :

cnms <- c("Nam1","Nam2","Nam3")

To create an empty data frame with the above variable names, first create a data.frame object:

emptydf <- data.frame()

Now call zeroth element of every column, thus creating an empty data frame with the given variable names:

for( i in 1:length(cnms)){
     emptydf[0,eval(cnms[i])]
 }

Answer 4

I have come across the same problem and have a cleaner solution. Instead of creating an empty data.frame you can instead save your data as a named list. Once you have added all results to this list you convert it to a data.frame after.

For the case of adding features one at a time this works best.

mylist = list()
for(column in 1:10) mylist$column = rnorm(10)
mydf = data.frame(mylist)

For the case of adding rows one at a time this becomes tricky due to mixed types. If all types are the same it is easy.

mylist = list()
for(row in 1:10) mylist$row = rnorm(10)
mydf = data.frame(do.call(rbind, mylist))

I haven't found a simple way to add rows of mixed types. In this case, if you must do it this way, the empty data.frame is probably the best solution.

Answer 5

Here a solution if you want an empty data frame with a defined number of rows and NO columns:

df = data.frame(matrix(NA, ncol=1, nrow=10)[-1]

Answer 6

Just create a data frame of empty vectors:

collect1 <- data.frame(id = character(0), max1 = numeric(0), max2 = numeric(0))

But if you know how many rows you're going to have in advance, you should just create the data frame with that many rows to start with.