Redis LREM Command Explained

In Redis, we can use the LREM command to remove one or more elements from a list. The number of elements removed depends on the arguments we pass.

Syntax

The syntax goes like this:

LREM key count element

Suppose we create a list like this:

RPUSH animals Cat Dog Horse Cat Dog Cat Monkey Dog Cat Dog Buffalo

Result:

(integer) 11

Let’s take a look at the list:

LRANGE animals 0 -1

Result:

 1) "Cat"
 2) "Dog"
 3) "Horse"
 4) "Cat"
 5) "Dog"
 6) "Cat"
 7) "Monkey"
 8) "Dog"
 9) "Cat"
10) "Dog"
11) "Buffalo"

Now let’s use the LREM command to remove the first two occurrences of Cat from the list:

LREM animals 2 "Cat"

Result:

(integer) 2

We can see that two elements were removed because the command returned an integer reply of 2.

We can verify this by taking a look at the list again:

LRANGE animals 0 -1

Result:

1) "Dog"
2) "Horse"
3) "Dog"
4) "Cat"
5) "Monkey"
6) "Dog"
7) "Cat"
8) "Dog"
9) "Buffalo"

The first two occurrences of Cat have been removed as expected.

Specifying a negative position removes the elements from the tail of the list:

LREM animals -2 "Dog"

Result:

(integer) 2

We can see that two elements were removed because the command returned an integer reply of 2.

When we check the list, we can see that they were removed from the tail:

LRANGE animals 0 -1

Result:

1) "Dog"
2) "Horse"
3) "Dog"
4) "Cat"
5) "Monkey"
6) "Cat"
7) "Buffalo"

We can use zero (0) to remove all occurrences of the specified element:

LREM animals 0 "Dog"

Result:

(integer) 2

In this case, there were two matching elements and both were removed.

We can verify this by looking at the list’s contents:

LRANGE animals 0 -1

Result:

1) "Horse"
2) "Cat"
3) "Monkey"
4) "Cat"
5) "Buffalo"

Non-existent keys are treated as empty lists and return 0:

LREM nonexistentkey 3 "Cat"

Result:

(integer) 0