A question about enlist function

Community Support
1

Hi,

I’m currently reading q for Mortals chapter 3, which talks about how to create a single item list. Below is the code:

singleton:enlist 1 2 3

When counting the number of element, it returns 1

count singleton 1

However, when I tried to print out singleton, I got all three element. 

singleton 1 2 3

I don’t understand now. Shouldn’t the list only contain 1?

Thanks!

Jerry

2

the stringyify for the console tries to make the result more readable.
If you want to see the full underlying structure of the result, use 0N!

e.g.

q)0N!singleton;

,1 2 3

where the , means enlist.

3

Hi Charles,

I have same question as Jerry. But your comments does not provide much clarification. Can you please elaborate more?

A singlton should have only one element in the list. but we can assign multiple atoms to a singlton list.

I don’t see any difference in the output of multi-element list and singleton.

q)multi:(1 2 3)q)singleton:enlist 1 2 3q)multi1 2 3q)singleton1 2 3

Please clarify. Thanks.

4

If you’d like a more explicit result, use 0N!

eg

 0N!singleton

5

Q console does not print the actual structure but format it so that it becomes more readable. To view actual structure, use 0N!

  q) 0N!multi;
  1 2 3    / list of 3 items

q) 0N!singleton;
 , 1 2 3   / comma shows that its  a list with one item which is again a list of 3 items

6

Ok, now it is a bit clear.

7

The Borror book isn’t very clear on this but enlist does more than just create a singleton from an atom.  It increases the rank of an atom or a list by one by essentially prepending a 1 to its “shape” vector.

E.g.

enlist enlist 5

creates a simulated 1x1 matrix.

Question:

APL2 has a pretty good DISPLAY function…is 0N! the best tool for displaying the structure of a list in Q?