LREM for element removal in Redis - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the LREM command do in Redis?

LREM removes elements from a list that match a given value. You specify how many matching elements to remove and the value to remove.

intermediate

How does the count parameter affect the LREM command?

The count parameter controls how many matching elements to remove: positive count removes from head to tail, negative count removes from tail to head, zero removes all matching elements.

beginner

Syntax of the LREM command?

LREM key count value Example: LREM mylist 2 "apple" removes up to 2 occurrences of "apple" from the list named mylist.

beginner

What happens if count is zero in LREM?

If count is zero, LREM removes all elements equal to the given value from the list.

beginner

Can LREM remove elements that do not exist in the list?

No, LREM only removes elements that match the value. If no elements match, the list remains unchanged and the command returns 0.

What does LREM mylist 3 "orange" do?

A Removes up to 3 occurrences of "orange" from the head of mylist

B Removes all occurrences of "orange" from mylist

C Removes 3 elements from the tail of mylist regardless of value

D Adds 3 "orange" elements to mylist

LREM with positive count removes up to that many matching elements from head to tail.

What does LREM mylist -2 "banana" do?

A Removes all "banana" elements from mylist

B Removes 2 "banana" elements from the head of mylist

C Removes 2 "banana" elements from the tail of mylist

D Removes 2 elements from mylist regardless of value

Negative count removes matching elements starting from the tail.

If count is zero in LREM, what happens?

A The list is cleared

B Only the first matching element is removed

C No elements are removed

D All matching elements are removed

Count zero means remove all matching elements.

What does LREM return?

A The removed elements themselves

B The number of elements removed

C The new length of the list

D Always 0

LREM returns how many elements it removed.

If the value does not exist in the list, what does LREM do?

A Does nothing and returns 0

B Removes the first element anyway

C Removes all elements

D Throws an error

If no matching elements exist, LREM does nothing and returns 0.

Explain how the count parameter affects the behavior of the LREM command in Redis.

Think about direction and how many elements are removed.

Describe a real-life example where you might use LREM to remove elements from a Redis list.

Imagine a list of things you want to update by removing some items.