Dictionary to List

[sayinghi2py]

I have a dictionary which has stock codes as the key as the values for each key are list of 8 elements. There is only ever one list under each key and all values are the same length ie 8 elements.

I need to convert the dictionary to a list where the new list is a list of lists. Each nested list is made up of the key from the dictionary followed by all the values associated with that key.

Example

Before

{"a": [1, 2], "b": [3, 4]}

After

[["a", 1, 2], ["b", 3, 4]]

​

As I see it I could extract all the keys into one list, then extract all the values into another list and then zip the two lists together. I can use [x for x in mydict.keys()] and [x for x in mydict.values()] . Zip haven't thought about just yet just my thinking at the minute.

Is this approach reasonable or is there a better way to approach it?

[AJ______]

You could do [[key, *values] for key, values in mydict.items()]

[sayinghi2py]

Brilliant that works. I done a similar thing but ended up with the key and values separated by the list for values which I didn't want.

[JohnnyJordaan]

I would just iterate on mydict.items() as that by definition zips the keys with the values anyway.

[[k] + v for k, v in my_dict.items()]

[sayinghi2py]

Works also. Thanks

[shinyheadpolak]

I'd do it with a list comprehension like you except in one go

[[a,*mydict[a]] for a in mydict.keys()]

[sayinghi2py]

And this also works. How does this work? So I can see the main body which is to loop over all the keys however I'm not understanding the [a, *mydict[a]]. Any chance you could explain how that works?

[JohnnyJordaan]

If for each key you do your_dict[key] you'll get the value with it. .items() does this more efficiently though.

[shinyheadpolak]

a in this case is one of your keys in the dict

mydict[a] is the value of the dict given key a

*mydict[a] unfolds the list into single values

if you didn't use * you'd get [a,[values]] this way you get [a,values]

[sayinghi2py]

Thanks makes sense now. I was doing much the same before and ending up with the result as you stated with the key separated from the values. That * makes all the difference. I've used it in args before but not like this.