CODEWITHSUNDEEP
rdataframe
Khurram Majeed
Khurram Majeed

Reputation: 2391

Create empty data.frame with column names

I am trying to create a empty data frame with two columns and unknown number of row. I would like to specify the names of the columns. I ran the following command

dat <- data.frame("id"=numeric(),"nobs"=numeric())

I can test the result by running

> str(dat)
'data.frame':   0 obs. of  2 variables:
 $ id  : num 
 $ nobs: num

But later on when I insert data into this data frame using rbind in the following command, the names of the columns are also changed

  for (i in id) {
    nobs = nrow(na.omit(read.csv(files_list[i])))
    dat = rbind(dat, c(i,nobs))
  }

After for loop this is the value of dat

dat
  X3 X243
1  3  243

And str command shows the following

str(dat)

'data.frame':   1 obs. of  2 variables:
 $ X3  : num 3
 $ X243: num 243

Can any one tell why are the col names in data frame change

EDIT:

My lazy solution to fix the problem is to run the follwing commands after for loop that binds data to my data.frame

names(dat)[1] = "id"
names(dat)[2] = "nobs"

Upvotes: 16

Views: 33672

Answers (4)

user3662777
user3662777

Reputation: 31

dat = data.frame(col1=numeric(), col2=numeric())  

...loop
    dat[, dim(dat)[1] + 1] = c(324, 234)

This keeps the column names

Upvotes: 2

Alexander
Alexander

Reputation: 490

You should try specify your column names inside the rbind():

dat = rbind(dat, data.frame("id" = i, "nobs" = nobs))

Upvotes: 1

patterja
patterja

Reputation: 1

I would change how you're appending the data to the data frame. Since rbind seems to remove the column names, just replace the indexed location. 

dat <- data.frame("id"=numeric(),"nobs"=numeric())  

for (i in id) {
   dat[i,] <- nrow(na.omit(read.csv(files_list[i])))

 }

FYI, Default data frame creation converts all strings to factors, not an issue here, since all your data formats are numeric. But if you had a character(), you might want to turn off the default stringsAsFactors=FALSE, to append character lists.

Upvotes: 0

MrFlick
MrFlick

Reputation: 206167

Interestingly, the rbind.data.frame function throws away all values passed that have zero rows. It basically happens in this line

allargs <- allargs[nr > 0L]

so passing in a data.frame with no rows, is really like not passing it in nothing at all. Another good example why it's almost always a bad idea to try to build a data.frame row-by-row. Better to build vectors and then combine into a data.frame only when done.

Upvotes: 10

Related Questions