startsWith

Determine if strings 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.

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

Examples

Detect Text at Start of String

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 = 2x3 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 = 2x3 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 = 2x1 string
    "data-analysis.ppt"
    "data.tar"

Detect Starts of Paths Using Pattern

Since R2020b

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 = 3x1 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 = 3x1 logical array

   1
   1
   0

Display the matching file names.

str(TF)

ans = 2x1 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

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 = 1x4 string
    "abstract.docx"    "data.tar.gz"    "mycode.m"    "results.ptx"

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

TF = 1x4 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 = 1x2 string
    "abstract.docx"    "data.tar.gz"

Ignore Case When Testing Start of String

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 = 1x4 string
    "DATA.TAR.GZ"    "data.xlsx"    "SUMMARY.PPT"    "tmp.gz"

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

TF = 1x4 logical array

   1   1   0   0

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

str(TF)

ans = 1x2 string
    "DATA.TAR.GZ"    "data.xlsx"

Determine If Character Vector Starts with Substrings

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

Input Arguments

str — Input text

string array | character vector | cell array of character vectors

Input text, specified as a string array, character vector, or cell array of character vectors.

pat — Search pattern

string array | character vector | cell array of character vectors | pattern array (since R2020b)

Search pattern, specified as one of the following:

• String array

• Character vector

• Cell array of character vectors

• pattern array (since R2020b)

Extended Capabilities

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.

Thread-Based Environment

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

This 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™.

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

Version History

Introduced in R2016b