Storing Lists in Redis: Modification Commands

In the previous lesson, we looked at a few commands used to insert lists into the Redis database. In this lesson, we will look at how we can modify a List present in the database.

LLEN command

The LLEN command is used to find the length of the list, as shown below.

LLEN key

LINDEX command

The LINDEX command is used to find the element at a particular index in the list.

LINDEX key index

In the index below, we are fetching the value at index 1.

Please note that the index starts at 0.

LSET command

The LSET command is used to update the value at a given index.

In the example below, we have bmw at the $0^{th}$ index. We will change it to mercedes using the lset command.

LSET key index value

LPUSHXcommand

The lpushx command adds an element to the head of the list if the list exists.

LPUSHX key value

In the example below, we will use the lpushx command for a key that does not exist, i.e., toyota. It will do nothing.

LINSERT command

This command is useful if we need to insert an element before a particular element. Let’s say, we need to add the first ten natural numbers in a list. We added them but forgot to add number 6, as shown below:

We have forgotten to add 6, which we need to add before 5. Remember: the elements are added in reverse order in the list since we are inserting at the head.

linsert key before/after pivot value

The pivot is the value before which we need to insert the number.

We will use this command to insert 6 in the list.