I'm very excited about the brand new [`Dataset`](http://reference.wolfram.com/language/ref/Dataset.html) function. I have played with it in [Wolfram Cloud][1], and haven't figured out how can I add a new column into an existing `Dataset`. Here is an example: data={<|"col1"->1,"col2"->2|>,<|"col1"->3,"col2"->4|>,<|"col1"->5,"col2"->6|>}; ds=Dataset[data] Now I can play with `ds` columns. For example, I can easily make calculations between columns using they names like: ds[All, (#col1+#col2&)] > {3, 7, 11} Another way is: ds[All, <|"col3"-> (#col1+#col2&)|>] > <|col3->3,col3->7,col3->11|> Now, how can I update `ds`, to append the brand new calculated column as "col3"? I tried: Join[ds,ds[All, <|"col3"-> (#col1+#col2&)|>],2] without success. It would be magic if I could just do something like: ds[All, "col3"]=ds[All, (#col1+#col2&)] But do not work either. [1]: http://www.wolframcloud.com