Create new dataframe from existing dataframe dynamically

Question

I have to create a new dataframe from a data frame that I don't know apriori.

The new dataframe should have the same structure as the old, but it should be empty.

Example

Let's suppose that the old data frame is the following:

> c1 = c(1,2,3)
> c2 = c("str1", "str2", "str3")
> c3 = c(3.2, 2.4, 5.6)
> m <- data.frame(c1,c2,c3)
> m
  c1   c2  c3
1  1 str1 3.2
2  2 str2 2.4
3  3 str3 5.6
> names(m) <- c("var1", "var2", "var3")
> m
  var1 var2 var3
1    1 str1  3.2
2    2 str2  2.4
3    3 str3  5.6

The new data frame should be like this:

newDat <- data.frame("var1" = as.numeric(), "var2" = as.character(), "var3" = as.numeric())

The point is that I don't know how the existing data frame (m) is made

Spacedman · Accepted Answer · 2016-05-07 10:52:49Z

6

Just take no rows from the original data frame:

> testDat = m[FALSE,]

There is a slight difference between that and your newDat example, because my testDat has a factor column which still has the levels from the original factor:

> str(testDat)
'data.frame':   0 obs. of  3 variables:
 $ var1: num 
 $ var2: Factor w/ 3 levels "str1","str2",..: 
 $ var3: num

If that's not a problem then job done, if it is a problem then you probably need to loop over the variables and reset any factors...

answered May 7, 2016 at 10:52

Spacedman

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1 Comment

G. Cocca Over a year ago

..or just use m <- data.frame(c1,c2,c3, stringsAsFactors = FALSE) in your old dataframe. Then using @Spacedman solution you will maintain the character class for testDat$var2 object. But this of course depends on your real dataset

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