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Mathematica > Core Language > Functional Programming > Functional Iteration >

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Built-in Mathematica Symbol

LengthWhile

LengthWhile[list, crit]
gives the number of continuous elements e_i starting at the beginning of list for which crit[e_i] is True.

Find the length of the run of elements below 10:

Elements of the list can be any expression:

Use on an expression with head f:

The result is the same as for a list of the values:

Find the length of the run of digits in

before a 7 occurs:

LengthWhile gives the length of the result from TakeWhile:

LengthWhile is equal to Length if crit[e_i] is True for all elements:

Otherwise it is 1 less than the first position for which crit[e_i] is not True:

The count terminates for any value of crit[e_i] that is not True: