problem with 'extract' function

3 次查看（过去 30 天）
Damian Maxwell
Damian Maxwell 2021-1-30
评论： dpb 2021-2-3
I am trying to extract characters from a string at a specific position using the 'extract' function.
However, even when entering the example code into my matlab program I get the error
Undefined function 'extract' for input arguments of type 'string'.
Can somebody help with this?
Matlab help page:
https://au.mathworks.com/help/matlab/ref/extract.html?s_tid=srchtitle
Section: Extract Character at Numeric Position
Create a string.
str = "All's well that ends well"
Extract the first character in the string.
extract(str,1)
From the command window:
>> str = "All's well that ends well"
str =
"All's well that ends well"
>> extract(str,1)
Undefined function 'extract' for input arguments of type 'string'.
Thanks!

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回答（2 个）

Star Strider
Star Strider 2021-1-30
The extract function was introduced in R2020b. If you have an earlier version/release, you need to upgrade to be able to use it. If you have R2020b and are still unable to use extract, run these commands:
restoredefaultpath
rehash toolboxcache
from a script or your Command Window and then try running it again. If you are still having problems after that, Contact Support.
dpb
dpb 2021-1-30
What do you get when you type
ver
at command line?
extract wasn't introduced until just now in R2020b so if you have a release earlier than that, you'll either have to upgrade or use the {} notation to get to the underlying char() string inside the string class string...
>> str = "All's well that ends well"
Extract the first character in the string.
extract(str,1)
str =
"All's well that ends well"
Unrecognized function or variable 'Extract'.
>> str{:}(1)
ans =
'A'
>>
  2 个评论
Damian Maxwell
Damian Maxwell 2021-2-3
Thanks DB. Your alternative method works.
dpb
dpb 2021-2-3
That was the only way to extract a substring from a string variable prior to R2020b that released extract into the wild.

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