keys

Keys of dictionary

Since R2022b

Syntax

k = keys(d)

k = keys(d,'cell')

Description

k = keys(d) returns an N-by-1 array of keys from the specified dictionary, where N is the number of entries in the dictionary. Keys are returned in the order in which the entries were added to the dictionary.

k = keys(d,'cell') optionally return the keys as a cell array.

Examples

Query Keys of Dictionary

Create a dictionary containing three key-value pairs that map numbers to strings.

names = ["Unicycle" "Bicycle" "Tricyle"];
wheels = [1 2 3];
d = dictionary(wheels,names)

d =

  dictionary (double ⟼ string) with 3 entries:

    1 ⟼ "Unicycle"
    2 ⟼ "Bicycle"
    3 ⟼ "Tricyle"

Use keys to return an array containing the keys stored in the dictionary.

k = keys(d)

k = 3×1

     1
     2
     3

Loop over and display each key of the dictionary.

for currentKey = keys(d)'
    disp("key: " + currentKey)
end

key: 1
key: 2
key: 3

Return Keys of Dictionary as Cell Array

Create a dictionary containing three key-value pairs that map numbers to strings.

names = ["Unicycle" "Bicycle" "Tricyle"];
wheels = [1 2 3];
d = dictionary(wheels,names)

d =

  dictionary (double ⟼ string) with 3 entries:

    1 ⟼ "Unicycle"
    2 ⟼ "Bicycle"
    3 ⟼ "Tricyle"

Use keys with the optional input "cell" to return an array containing the keys stored in the dictionary as a cell array.

k = keys(d,"cell")

k=3×1 cell array
    {[1]}
    {[2]}
    {[3]}

Input Arguments

d — Dictionary

dictionary object

Dictionary, specified as a dictionary object. If d is unconfigured, keys throws an error.

Output Arguments

k — Dictionary keys

N-by-1 array

Dictionary keys, returned as an N-by-1 array of keys from the specified dictionary, where N is the number of entries in the dictionary. Keys are returned in the order in which the entries were added to the dictionary.

Extended Capabilities

C/C++ Code Generation

Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

• If the code generator is unable to return the dictionary keys as an array, code generation fails. In these situations, use the "cell" argument to return dictionary keys as a cell array.

• If you use it, the "cell" argument must be a constant at code generation time.

• The code generator does not treat a dictionary as a constant, even if the dictionary is constant at code generation time. This means that the keys function does not return a constant. You cannot pass the output of the keys function to a function that requires constant inputs. You cannot use the output of the keys function for operations that require constants, such as indexing into a heterogeneous cell array. The code generator also cannot perform optimizations that depend on constants, such as constant folding, on the output of the keys function.

For additional considerations that apply when generating C/C++ code for MATLAB^® dictionaries, see Dictionary Limitations for Code Generation (MATLAB Coder).

GPU Code Generation

Generate CUDA® code for NVIDIA® GPUs using GPU Coder™.

Refer to the usage notes and limitations in the C/C++ Code Generation section. The same usage notes and limitations apply to GPU code generation.

Version History

Introduced in R2022b

R2024b: Code generation support

You can generate C/C++ code for the dictionary keys function.