R factors and df

New to R, trying to iterate through a DF and see if the data type of the row is empty ('') If so, I would like to add a factor and if not then do nothing.

My expected output is for df$data_type[i] to contain 25 Levels: BIGINT BOOLEAN BYTEINT CHAR DATE DATETIME DECIMAL DOUBLE FLOAT INT NUMBER NUMERIC OBJECT REAL SMALLINT STRING ... VARIANT. I am using this DF to render a Rhandsontable and I need the empty data type cols to have a drop down which contains the items in the factor. The dropdown will be used for users to select only a valid data type from the data_type_vals.

sample df vals

               logical_name physical_name data_type length
1     AGENT PERIPHERAL NAME  AGT_PRPHL_NM   VARCHAR   32.0
2 AGENT SCHEDULE IDENTIFIER   AGT_SCHD_ID    NUMBER   <NA>
3                  DUE DATE        DUE_DT  



foo <- function(df){
  data_type_vals <- c("BIGINT", "BOOLEAN", "BYTEINT", "CHAR", "DATE", "DATETIME", "DECIMAL", "DOUBLE", "FLOAT", "INT", "NUMBER", "NUMERIC", "OBJECT", "REAL", "SMALLINT", "STRING", "TEXT", "TIME", "TIMESTAMP", "TIMESTAMP_LTZ", "TIMESTAMP_NTZ", "TIMESTAMP_TZ", "VARBINARY", "VARCHAR", "VARIANT")
    df <- mutate_all(df, funs(toupper))

dput(head(df))

    if(nrow(df)>=1){
      for(i in 1:nrow(df)){
        if(df$data_type[i] == ''){
#this line is not working
          df$data_type[i] <- factor('', levels = data_type_vals)   
#this works but replaces all 
df$data_type <- factor('', levels = data_type_vals)   
        }
      }
    }
   dput(head(df))    
}

Rhandsontable image/the red box should be a dropdown with the factor values