Commandslpos
LPOS
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Get the index of a value
The usage is lpos key value.
Indexes start at 0 from the head (left).
Example
| Command> | rpush mylist A B C 1 2 3 C C |
| Result> | 8 |
| Command> | lpos mylist A |
| Result> | (integer) 0 |
| Command> | lpos mylist C |
| Result> | (integer) 2 The index of the first C is returned. |
RANK option: specify which match to find
To find the second C, use RANK 2.
A negative rank searches from the tail (right).
Example
| Command> | lpos mylist C RANK 2 |
| Result> | (integer) 6 |
| Command> | lpos mylist C RANK -1 |
| Result> | (integer) 7 |
COUNT option: specify how many matches to return
When the same value appears more than once, specify how many matches to return. Specify 0 to find all of them.
Example
| Command> | lpos mylist C COUNT 2 |
| Result> | 1) (integer) 2 2) (integer) 6 |
| Command> | lpos mylist C COUNT 0 |
| Result> | 1) (integer) 2 2) (integer) 6 3) (integer) 7 |
MAXLEN option: limit how many elements to scan
If the list has a very large number of elements,
finding a value can take time.
Use this to limit how many elements are scanned so the query does not take too long.
You can use the RANK, COUNT, and MAXLEN options together.
Example
| Command> | lpos mylist C COUNT 0 MAXLEN 3 |
| Result> | 1) (integer) 2 |
| Command> | lpos mylist C COUNT 0 MAXLEN 7 |
| Result> | 1) (integer) 2 2) (integer) 6 |
Notes
If the value is not found, nil is returned.
If the COUNT option is used, (empty array) is returned.
Example
| Command> | lpos mylist D |
| Result> | (nil) |
| Command> | lpos mylist D COUNT 0 |
| Result> | (empty array) |
Syntax
LPOS key element [RANK rank] [COUNT num-matches] [MAXLEN len]
- Available since version 6.0.6.
- Time complexity is O(N). N is the number of values or the count specified by MAXLEN.
| << LINDEX | LPOS | LSET >> |
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