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

Answer 1

This question didn't specifically address my concerns (outlined here) but in case anyone wants to do this with a parameterized number of columns and no coercion:

> require(dplyr)
> dbNames <- c('a','b','c','d')
> emptyTableOut <- 
    data.frame(
        character(), 
        matrix(integer(), ncol = 3, nrow = 0), stringsAsFactors = FALSE
    ) %>% 
    setNames(nm = c(dbNames))
> glimpse(emptyTableOut)
Observations: 0
Variables: 4
$ a <chr> 
$ b <int> 
$ c <int> 
$ d <int>

As divibisan states on the linked question,

...the reason [coercion] occurs [when cbinding matrices and their constituent types] is that a matrix can only have a single data type. When you cbind 2 matrices, the result is still a matrix and so the variables are all coerced into a single type before converting to a data.frame

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.

Answer 3

You can do it without specifying column types

df = data.frame(matrix(vector(), 0, 3,
                dimnames=list(c(), c("Date", "File", "User"))),
                stringsAsFactors=F)

Answer 4

I created empty data frame using following code

df = data.frame(id = numeric(0), jobs = numeric(0));

and tried to bind some rows to populate the same as follows.

newrow = c(3, 4)
df <- rbind(df, newrow)

but it started giving incorrect column names as follows

  X3 X4
1  3  4

Solution to this is to convert newrow to type df as follows

newrow = data.frame(id=3, jobs=4)
df <- rbind(df, newrow)

now gives correct data frame when displayed with column names as follows

  id nobs
1  3   4 

Answer 5

Say your column names are dynamic, you can create an empty row-named matrix and transform it to a data frame.

nms <- sample(LETTERS,sample(1:10))
as.data.frame(t(matrix(nrow=length(nms),ncol=0,dimnames=list(nms))))