LengthWhile [list,crit]
gives the number of contiguous elements ei starting at the beginning of list for which crit[ei] is True .
LengthWhile
LengthWhile [list,crit]
gives the number of contiguous elements ei starting at the beginning of list for which crit[ei] is True .
Details
- LengthWhile can be used on an object with any head, not necessarily List .
Examples
open all close allBasic Examples (1)
Find the length of the run of elements below 10:
Scope (1)
Elements of the list can be any expression:
Generalizations & Extensions (1)
Use on an expression with head f:
The result is the same as for a list of the values:
Applications (1)
Find the length of the run of digits in before a 7 occurs:
Properties & Relations (3)
LengthWhile gives the length of the result from TakeWhile :
LengthWhile is equal to Length if crit[ei] is True for all elements:
Otherwise it is 1 less than the first position for which crit[ei] is not True :
Possible Issues (1)
The count terminates for any value of crit[ei] that is not True :
See Also
Tech Notes
Related Guides
Text
Wolfram Research (2007), LengthWhile, Wolfram Language function, https://reference.wolfram.com/language/ref/LengthWhile.html (updated 2008).
CMS
Wolfram Language. 2007. "LengthWhile." Wolfram Language & System Documentation Center. Wolfram Research. Last Modified 2008. https://reference.wolfram.com/language/ref/LengthWhile.html.
APA
Wolfram Language. (2007). LengthWhile. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/LengthWhile.html
BibTeX
@misc{reference.wolfram_2025_lengthwhile, author="Wolfram Research", title="{LengthWhile}", year="2008", howpublished="\url{https://reference.wolfram.com/language/ref/LengthWhile.html}", note=[Accessed: 05-December-2025]}
BibLaTeX
@online{reference.wolfram_2025_lengthwhile, organization={Wolfram Research}, title={LengthWhile}, year={2008}, url={https://reference.wolfram.com/language/ref/LengthWhile.html}, note=[Accessed: 05-December-2025]}