Create an empty data.frame

Question

I'm trying to initialize a data.frame without any rows. Basically, I want to specify the data types for each column and name them, but not have any rows created as a result.

The best I've been able to do so far is something like:

df <- data.frame(Date=as.Date("01/01/2000", format="%m/%d/%Y"),                   File="", User="", stringsAsFactors=FALSE) df <- df[-1,] 

Which creates a data.frame with a single row containing all of the data types and column names I wanted, but also creates a useless row which then needs to be removed.

Is there a better way to do this?

Answer 1

Just initialize it with empty vectors:

df <- data.frame(Date=as.Date(character()),                  File=character(),                   User=character(),                   stringsAsFactors=FALSE)  

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Here's an other example with different column types :

df <- data.frame(Doubles=double(),                  Ints=integer(),                  Factors=factor(),                  Logicals=logical(),                  Characters=character(),                  stringsAsFactors=FALSE)  str(df) > str(df) 'data.frame':   0 obs. of  5 variables:  $ Doubles   : num   $ Ints      : int   $ Factors   : Factor w/ 0 levels:   $ Logicals  : logi   $ Characters: chr  

N.B. :

Initializing a data.frame with an empty column of the wrong type does not prevent further additions of rows having columns of different types.
This method is just a bit safer in the sense that you'll have the correct column types from the beginning, hence if your code relies on some column type checking, it will work even with a data.frame with zero rows.

Answer 2

If you already have an existent data frame, let's say df that has the columns you want, then you can just create an empty data frame by removing all the rows:

empty_df = df[FALSE,] 

Notice that df still contains the data, but empty_df doesn't.

I found this question looking for how to create a new instance with empty rows, so I think it might be helpful for some people.