问题
For example, I have this list:
test:(8;12;15;19;10)
How may I select elements 2 to 4?
When I try list[2;4] it doesn't work for me.
回答1:
indexing a list is by far the fastest way.
q)a
8 1 9 5 4 6 6 1 8 5 4 9 2 7 0 1 9 2 1 8 8 1 7 2 4 5 4 2 7 8 5 6 4 1 3 3 7 8 2..
q)\t do[100000;2 3 sublist a]
109
q)\t do[100000;a 2 3 4]
15
So just follow your list with a list of indexes. BTW you can create indexes with til
q)til 2
0 1
q)2+til 2
2 3
回答2:
You can use sublist for this
test:(8;12;15;19;10);
2 3 sublist test
This will return three elements from the list starting at index 2.
回答3:
As answered by Manish, til is the best bet here. You can define a simple function range using til to give the index range :
q)test:(8;12;15;19;10)
q)range:{x+til 1+abs[y-x]} //include the start and end index
q)test range[2;4]
15j, 19j, 10j
来源：https://stackoverflow.com/questions/28525768/how-to-get-range-of-elements-in-a-list-in-kdb