List Slicing in DolphinDB

What will you learn?

Explore the world of list slicing in DolphinDB and master the art of extracting specific elements from a list effortlessly.

Introduction to the Problem and Solution

When dealing with data, it’s often necessary to work with subsets of lists or arrays. List slicing comes to the rescue by allowing us to extract particular elements based on their indices. In DolphinDB, similar to Python, we can achieve this using square brackets [] for indexing.


# Example showcasing list slicing in DolphinDB

// Create a sample list
list = [1, 2, 3, 4, 5]

// Slice the list from index 1 to index 3 (exclusive)
sliced_list = list[1:3]

// Display the sliced_list

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In the provided code snippet: – Initialize a sample list containing integers. – Utilize square brackets with start and end indices separated by : for list slicing. – The slice operation [1:3] retrieves elements starting from index 1 up to (but excluding) index 3. – The resulting sliced_list will contain elements [2, 3].

    How do I slice lists in DolphinDB?

    To slice lists in DolphinDB, use square brackets [start_index:end_index], where start_index is inclusive and end_index is exclusive.

    Can I omit either the start or end index while slicing?

    Yes, you can omit either the start or end index when slicing lists. For instance: – Omitting the start index ([:end_index]) begins from the beginning of the list. – Omitting the end index ([start_index:]) slices until the end of the list.

    Are negative indices supported for slicing in DolphinDB?

    Absolutely! Negative indices are supported for slicing lists in DolphinDB. They count backward from the end of the list (-1 refers to the last element).

    How can I step through a list while slicing?

    You can introduce a step value after another colon (:) within square brackets. For example: [start:end:step].

    Is there any way to reverse a list using slicing?

    Certainly! To reverse a list via slicing in DolphinDB, set -1 as the step value along with empty start and end indices like so: [::-1].

    Does DolphinDB support multi-dimensional array/list slices like NumPy arrays?

    No, unlike NumPy arrays which support multi-dimensional slices with comma-separated tuples (x,y), Dolphindb only supports single-dimensional slices.


    Mastering list slicing is crucial for efficient data manipulation tasks. By grasping how to perform precise slices on lists using indexes effectively streamlines data processing workflows.

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