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This article introduces the knowledge of "sorting out common commands of Redis list types". In the operation of actual cases, many people will encounter such a dilemma, so let the editor lead you to learn how to deal with these situations. I hope you can read it carefully and be able to achieve something!

Redis common command list type

Add elements to both ends of the list

Lpush key value [value. ]

The lpush command is used to add an element to the left of the list, and returns the length of the list after adding the element.

Rpush key value [value. ]

The rpush command is used to add elements to the right of the list, and returns the length of the list after adding elements.

Pop elements from both ends of the list

Lpop key

The lpop command can pop up an element from the left side of the list, and the lpop command performs two steps: 1: remove the element on the left side of the list from the list; 2: return the value of the removed element

Rpop key

The rpop command pops up an element from the right side of the list, as above.

Get the number of elements in the list

Llen key

When the key does not exist, llen returns 0

Get the list fragment

Lrange key start stop

Get a fragment of the list and return that the index starts with 0 for all elements (including elements at both ends) from start to stop

Note: one difference between lrange and the method used to intercept array fragments in many languages is that the value returned by lrange contains the rightmost element

The lrange command also supports negative indexes. The table calculates the ordinal number from the right. For example,'- 1 'represents the first element on the right,'-2 'represents the second element on the right, and so on.

Delete the value specified in the list

Lrem key count value

The lrem command deletes the elements in the list whose previous count value is value, and the return value is the number of elements actually deleted. Depending on the count value, the lrem command is executed in a slightly different way

When count > 0, the lrem command deletes the elements whose previous count value is value from the left side of the list

When count < 0, the lrem command deletes the elements whose previous count value is value from the right side of the list

When count = 0, the lrem command deletes all elements with a value of value

Gets / sets the element value of the specified index

Lindex key index

The lindex command returns the element of the specified index. The index starts at 0. If index is negative, the index is calculated from the right. The index of the rightmost element is-1.

Lset key index value

Lset is a command that manipulates the list through the index. It assigns the element indexed to index to value.

Keep only the specified clips in the list

Ltrim key start end

The ltrim command deletes all elements outside the specified index range in the same way as the lrange command.

The ltrim command is often used with the lpush command to limit the number of elements in the list. For example, if we want to keep only the last 100 logs when logging, we can call the ltrim command again every time a new element is added.

Insert an element into the list

Linsert key before | after pivot value

The linsert command first looks from left to right in the list for an element with a value of pivot, and then decides whether to insert value before or after the element based on whether the second parameter is before or after, and if the command is successful, returns the length of the list after the insert operation is completed. Return-1 if pivot is not found. If key does not exist or is empty, return 0

Move elements from one list to another list R

Rpoplpush source destination

Rpoplpush first executes the rpop command before executing the lpush command. The rpoplpush command first pops up an element from the right side of the source list type key, then adds it to the left side of the destination list type key, and returns the value of this element, the whole process is atomic.

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