startsWith

R2026b

Determine if strings or category names start with pattern

Syntax

TF = startsWith(str,pat)

TF = startsWith(str,pat,IgnoreCase=true)

Description

TF = startsWith(str,pat) returns 1 (true) if str starts with the specified pattern, and returns 0 (false) otherwise.

If pat is an array containing multiple patterns, then startsWith returns 1 if it finds that str starts with any element of pat.

example

TF = startsWith(str,pat,IgnoreCase=true) ignores case when determining if str starts with pat.

example

Examples

collapse all

Detect Text at Start of String

Open Live Script

Create a string array that contains file names. Determine which file names start with the word data.

str = ["abstract.docx","data.tar","code.m"; ...
       "data-analysis.ppt","results.ptx","summary.ppt"]

str = 2×3 string
    "abstract.docx"        "data.tar"       "code.m"     
    "data-analysis.ppt"    "results.ptx"    "summary.ppt"

Return a logical array where the position of each element equal to 1 corresponds to the position of a string in str that starts with data.

pat = "data";
TF = startsWith(str,pat)

TF = 2×3 logical array

   0   1   0
   1   0   0

Display the file names that start with data. Index back into str using TF.

str(TF)

ans = 2×1 string
    "data-analysis.ppt"
    "data.tar"

Detect Starts of Paths Using Pattern

Open Live Script

Create a string array that has references to files, including full paths for local files and URLs for remote ones.

str = ["C:\Temp\MyReport.docx";
       "D:\Data\Experiment1\Trial1\Sample1.csv";
       "https://example.com/Slides.pptx"]

str = 3×1 string
    "C:\Temp\MyReport.docx"
    "D:\Data\Experiment1\Trial1\Sample1.csv"
    "https://example.com/Slides.pptx"

To find the paths that start with a drive letter, create a pattern that matches one letter followed by a colon.

pat = lettersPattern(1) + ":"

pat = pattern
  Matching:

    lettersPattern(1) + ":"

Determine which elements of str start with that pattern. The pattern pat does not match "https:" because lettersPattern(1) matches only one letter.

TF = startsWith(str,pat)

TF = 3×1 logical array

   1
   1
   0

Display the matching file names.

str(TF)

ans = 2×1 string
    "C:\Temp\MyReport.docx"
    "D:\Data\Experiment1\Trial1\Sample1.csv"

For a list of functions that create pattern objects, see pattern.

Test Start of String Against Multiple Substrings

Open Live Script

Create a string array that contains file names. Determine which file names start with either abstract or data.

str = ["abstract.docx","data.tar.gz","mycode.m","results.ptx"]

str = 1×4 string
    "abstract.docx"    "data.tar.gz"    "mycode.m"    "results.ptx"

pat = ["abstract","data"];
TF = startsWith(str,pat)

TF = 1×4 logical array

   1   1   0   0

Display the strings that start with either abstract or data. Index back into str using TF.

str(TF)

ans = 1×2 string
    "abstract.docx"    "data.tar.gz"

Ignore Case When Testing Start of String

Open Live Script

Create a string array that contains file names. Determine which file names start with data, ignoring case.

str = ["DATA.TAR.GZ","data.xlsx","SUMMARY.PPT","tmp.gz"]

str = 1×4 string
    "DATA.TAR.GZ"    "data.xlsx"    "SUMMARY.PPT"    "tmp.gz"

pat = "data";
TF = startsWith(str,pat,IgnoreCase=true)

TF = 1×4 logical array

   1   1   0   0

Display the strings that start with data. Index back into str using TF.

str(TF)

ans = 1×2 string
    "DATA.TAR.GZ"    "data.xlsx"

Determine If Character Vector Starts with Substrings

Open Live Script

Create a character vector that contains the name of a file. Determine if the name starts with different substrings.

chr = 'data-analysis.ppt'

chr = 
'data-analysis.ppt'

TF = startsWith(chr,'data')

TF = logical
   1

TF = startsWith(chr,'test')

TF = logical
   0

Determine If Category Names Start with String

Since R2026b

Open Live Script

Load data on electric utility outages in the United States as a table. Convert the Region variable to a categorical array.

T = readtable("outages.csv");
T.Region = categorical(T.Region);

Determine if the category names of Region start with "South". The startsWith function returns a logical array indicating which elements in the Region categorical array have category names that start with "South".

TF = startsWith(T.Region,"South",IgnoreCase=true)

TF = 1468×1 logical array

   1
   1
   1
   0
   0
   0
   0
   0
   0
   0
   1
   0
   1
   1
   0
      ⋮

Display only the rows of the table where the region starts with "South".

T(TF,:)

ans = 415×6 table
     Region         OutageTime        Loss     Customers     RestorationTime            Cause       
    _________    ________________    ______    __________    ________________    ___________________

    SouthWest    2002-02-01 12:18    458.98    1.8202e+06    2002-02-07 16:50    {'winter storm'   }
    SouthEast    2003-01-23 00:49    530.14    2.1204e+05                 NaT    {'winter storm'   }
    SouthEast    2003-02-07 21:15     289.4    1.4294e+05    2003-02-17 08:14    {'winter storm'   }
    SouthEast    2004-09-05 17:48    73.387         36073    2004-09-05 20:46    {'equipment fault'}
    SouthEast    2002-09-01 18:22    95.917         36759    2002-09-01 19:12    {'severe storm'   }
    SouthEast    2003-09-27 07:32       NaN    3.5517e+05    2003-10-04 07:02    {'severe storm'   }
    SouthEast    2004-12-06 23:18       NaN         37136    2004-12-14 03:21    {'winter storm'   }
    SouthEast    2002-12-12 18:08    46.918    1.0698e+05    2002-12-14 18:43    {'winter storm'   }
    SouthEast    2005-03-08 16:37    1339.2    4.3003e+05    2005-03-10 20:42    {'winter storm'   }
    SouthEast    2003-02-24 06:13         0             0    2003-02-24 21:18    {'attack'         }
    SouthEast    2005-05-07 00:07     65.95         47140    2005-05-07 09:26    {'thunder storm'  }
    SouthWest    2004-06-06 05:27    559.41      2.19e+05    2004-06-06 05:55    {'equipment fault'}
    SouthEast    2003-04-13 01:58    124.76        1.0142    2003-05-20 11:09    {'unknown'        }
    SouthEast    2002-07-14 21:32     90.83         60133    2002-07-14 23:53    {'thunder storm'  }
    SouthWest    2004-07-18 14:40    340.35    1.4963e+05    2004-07-26 23:34    {'severe storm'   }
    SouthEast    2003-09-05 20:15    1700.1    1.6393e+05    2003-09-10 19:59    {'thunder storm'  }
      ⋮

Input Arguments

collapse all

`str` — Input array
string array | character vector | cell array of character vectors | categorical array

Input array, specified as a string array, character vector, cell array of character vectors, or categorical array (since R2026b).

`pat` — Search pattern
string array | character vector | cell array of character vectors | `pattern` array

Search pattern, specified as one of the following:

String array
Character vector
Cell array of character vectors
pattern array

Extended Capabilities

expand all

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

The startsWith function fully supports tall arrays. For more information, see Tall Arrays.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

Usage notes and limitations:

str and pattern must be a string scalar, a character vector, or a cell array containing not more than one character vector.

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.

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`.

The startsWith function fully supports thread-based environments. For more information, see Run MATLAB Functions in Thread-Based Environment.

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

The startsWith function fully supports distributed arrays. For more information, see Run MATLAB Functions with Distributed Arrays (Parallel Computing Toolbox).

Version History

Introduced in R2016b

expand all

R2026b: Support for categorical arrays

The startsWith function now supports categorical arrays as the input array. You can use this function to determine whether elements in a categorical array have category names that start with a specified pattern.

startsWith

Syntax

Description

Examples

Detect Text at Start of String

Detect Starts of Paths Using Pattern

Test Start of String Against Multiple Substrings

Ignore Case When Testing Start of String

Determine If Character Vector Starts with Substrings

Determine If Category Names Start with String

Input Arguments

`str` — Input array
string array | character vector | cell array of character vectors | categorical array

`pat` — Search pattern
string array | character vector | cell array of character vectors | `pattern` array

Extended Capabilities

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

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

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`.

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

Version History

R2026b: Support for categorical arrays

See Also

Topics

startsWith

Syntax

Description

Examples

Detect Text at Start of String

Detect Starts of Paths Using Pattern

Test Start of String Against Multiple Substrings

Ignore Case When Testing Start of String

Determine If Character Vector Starts with Substrings

Determine If Category Names Start with String

Input Arguments

str — Input array string array | character vector | cell array of character vectors | categorical array

pat — Search pattern string array | character vector | cell array of character vectors | pattern array

Extended Capabilities

Tall Arrays Calculate with arrays that have more rows than fit in memory.

C/C++ Code Generation Generate C and C++ code using MATLAB® Coder™.

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

Thread-Based Environment Run code in the background using MATLAB® backgroundPool or accelerate code with Parallel Computing Toolbox™ ThreadPool.

Distributed Arrays Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.

Version History

R2026b: Support for categorical arrays

See Also

Topics

`str` — Input array
string array | character vector | cell array of character vectors | categorical array

`pat` — Search pattern
string array | character vector | cell array of character vectors | `pattern` array

Tall Arrays
Calculate with arrays that have more rows than fit in memory.

C/C++ Code Generation
Generate C and C++ code using MATLAB® Coder™.

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

Thread-Based Environment
Run code in the background using MATLAB® `backgroundPool` or accelerate code with Parallel Computing Toolbox™ `ThreadPool`.

Distributed Arrays
Partition large arrays across the combined memory of your cluster using Parallel Computing Toolbox™.