How i can create empty dataframe with column name where column is a vector any length
c("A","B","C")
Im try
df<-data.frame()
colnames(df)<-c("A","B")
But is not working
2 Answers
x <- LETTERS[1:3]
df <- as.data.frame(matrix(,0,length(x)))
names(df) <- x
str(df)
# 'data.frame': 0 obs. of 3 variables:
# $ A: logi
# $ B: logi
# $ C: logi
With OP's vector:
x <- c("field1","field2", "field3")
df <- as.data.frame(matrix(,0,length(x)))
names(df) <- x
str(df)
# 'data.frame': 0 obs. of 3 variables:
# $ field1: logi
# $ field2: logi
# $ field3: logi
8 Comments
Nikolay
For example im have vector c("field1","field2, filed3")
nicola
With a line:
as.data.frame(matrix(nrow=0,ncol=length(x),dimnames=list(NULL,x)))
RHertel
I believe that there are cases where this can be useful. Imagine for example the case where you want to generate a table (dataframe) where each row is the result of calculations performed on temporary data retrieved from an external source. In such a situation you may not know at the beginning the number of rows that your resulting data frame will have. I think that
rbinding each row, starting with an empty dataframe with named columns, would make sense there.
Roland
@RHertel No, guess a reasonable size, (over-)allocate that, grow in chunks only if needed, subset to the final size in the end.
nicola
@RHertel If you know the number of iterations (as one usually does), you allocate a
list before in which you put the data.frame returned from the external source. At the end of the loop, you rbind them all together with do.call. Or do like Roland suggested. |
You can try this:
df1 <- data.frame(matrix(vector(),ncol=3))
colnames(df1) <-c("A","B","C")
df1
#[1] A B C
#<0 rows> (or 0-length row.names)
df <- data.frame(A = numeric(n), B = character(n), C = logical(n))for anyn.data.frame(A = c(), B = c())str(data.frame(A = c(), B = c())) 'data.frame': 0 obs. of 0 variables