在数据帧R中插入NA值

Question

I want an empty data frame and later add row values to it. The way I create a data frame is the following:

result_df <- data.frame("Hospital" = character(), "State" = character(), stringsAsFactors = FALSE)

Then I add the first row:

result_df <- rbind(result_df, list("D W MCMILLAN MEMORIAL HOSPITAL", "AL"))

Just as extra information I show you the result of the following command:

str(result_df)

'data.frame':   1 obs. of  2 variables:
 $ X.D.W.MCMILLAN.MEMORIAL.HOSPITAL.: Factor w/ 1 level "D W MCMILLAN MEMORIAL HOSPITAL": 1
 $ X.AL.                            : Factor w/ 1 level "AL": 1

Then I add the next row to the data frame

result_df <- rbind(result_df, list("ARKANSAS METHODIST MEDICAL CENTER", "TX"))

and this is what I get:

Warning messages:
1: In `[<-.factor`(`*tmp*`, ri, value = "ARKANSAS METHODIST MEDICAL CENTER") :
  invalid factor level, NA generated
2: In `[<-.factor`(`*tmp*`, ri, value = "TX") :
  invalid factor level, NA generated

When I type result_df to see the content of the data frame this is the result:

  X.D.W.MCMILLAN.MEMORIAL.HOSPITAL. X.AL.
1    D W MCMILLAN MEMORIAL HOSPITAL    AL
2                              <NA>  <NA>

I guess this could be solved using stringAsFactors = FALSE, does any one have an idea about this problem?

Answer 1

The rbind function needs to have the same column names. If you created the data frame with the same column names, you can combine these data frames without NA.

result_df <- rbind(result_df, data.frame(Hospital = "D W MCMILLAN MEMORIAL HOSPITAL", 
                                         state = "AL",
                                         stringsAsFactors = FALSE))

result_df <- rbind(result_df, data.frame(Hospital = "ARKANSAS METHODIST MEDICAL CENTER", 
                                         state = "TX",
                                         stringsAsFactors = FALSE)) 

Here is the final output.

print(result_df)
                           Hospital state
1    D W MCMILLAN MEMORIAL HOSPITAL    AL
2 ARKANSAS METHODIST MEDICAL CENTER    TX

Answer 2

We can use rbindlist from data.table

library(data.table)
rbindlist(list(result_df, list("D W MCMILLAN MEMORIAL HOSPITAL", "AL")))
#                         Hospital State
#1: D W MCMILLAN MEMORIAL HOSPITAL    AL