I have a dataframe with five columns and 6 rows (actually they are many more, just trying to simplify matters):

```
One Two Three   Four    Five
Cat NA  NA  NA  NA
NA  Dog NA  NA  NA
NA  NA  NA  Mouse   NA
Cat NA  Rat NA  NA
Horse   NA  NA  NA  NA
NA NA NA NA NA

```

Now, I would like to coalesce all the information in a new single column ('Summary'), like this:

```
Summary
Cat
Dog
Mouse
Error
Horse
NA

```

Please note the 'Error' reported on the fourth Summary row, because two different values have been reported during the merging. I tried to look at the 'coalesce' function in the dplyr package, but it really desn't seem to do what I need.
Thanks in advance.

**Edited**: I added a 6th row to indicate that in case of all 'NA' in row, I would like to get 'NA' and not 'Errors' in my 'Summary' column. Sorry if this was not clear in my first post.