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LCS

Last updated 
LCS key1 key2 [LEN] [IDX] [MINMATCHLEN min-match-len] [WITHMATCHLEN]
Group
String
Complexity
O(N*M) where N and M are the lengths of the two strings
Arity
-3 (at least 3 words, counting the command name)
Flags
read-only
Keys
first 1, last 2, step 1
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LCS compares the strings at key1 and key2 and finds their longest common subsequence: the longest run of characters that appears in both, in the same order, but not necessarily next to each other. It is useful for diffing short texts or measuring how similar two values are. A missing key counts as an empty string.

Options

Section titled “Options”
Option Effect
LEN Return only the length of the subsequence.
IDX Return the positions of the matching ranges in both strings, and the length.
MINMATCHLEN min-match-len With IDX, leave out ranges shorter than this.
WITHMATCHLEN With IDX, add the length of each range to its entry.

LEN and IDX cannot be combined. With IDX, ranges are listed from the end of the strings towards the start, and each position pair is the first and last offset of the range, both included.

Return value

Section titled “Return value”
Case RESP2 RESP3
No option Bulk string: the subsequence Bulk string
LEN Integer: its length Integer
IDX Array ["matches", [...], "len", length] Map with the keys matches and len

Each entry in matches is an array of two ranges, [start1, end1] in the first string and [start2, end2] in the second, followed by the range length when WITHMATCHLEN is given.

Errors:

  • ERR The specified keys must contain string values when either key holds another type.
  • ERR If you want both the length and indexes, please just use IDX. when LEN and IDX are both given.
  • ERR Insufficient memory, transient memory for LCS exceeds proto-max-bulk-len when the strings are too long to compare.
  • ERR syntax error for an unknown option.

Examples

Section titled “Examples”
127.0.0.1:6379> MSET a "redwood" b "deadwood"
OK
127.0.0.1:6379> LCS a b
"edwood"
127.0.0.1:6379> LCS a b LEN
(integer) 6
127.0.0.1:6379> LCS a b IDX MINMATCHLEN 2 WITHMATCHLEN
1) "matches"
2) 1) 1) 1) (integer) 2
         2) (integer) 6
      2) 1) (integer) 3
         2) (integer) 7
      3) (integer) 5
3) "len"
4) (integer) 6

Compatibility

Section titled “Compatibility”

Same as Redis 7 and Valkey 8.

See also

Section titled “See also”

GETRANGE, STRLEN, GET