How do I replace elements in a list matching a pattern?

Usual approach would be to use ReplaceAll:

list = {0, 1, 1, 1, 2, 2, 2, 6};
list/.{x_?(# > 1 &) -> 1}

A slick approach would be

Boole /@ GreaterEqualThan[1] /@ list

Or even

Map[Min[#, 1] &, list]

Faster approach would be to use:

Unitize[list]
Clip[list]

All of them would give you:

{0, 1, 1, 1, 1, 1, 1, 1}

I just ran list = Table[RandomInteger[10], 100000] and used Mr.Wizard's timeAvg function:

list /. {x_?(# > 1 &) -> 1} // timeAvg
Boole /@ GreaterEqualThan[1] /@ list // timeAvg
Map[Min[#, 1] &, l] // timeAvg
Unitize[l] // timeAvg
Clip[l] // timeAvg

0.0690836

0.0559747

0.00204779

0.000139352

0.00022492

I just googled "wolfram mathematica replace if". Based on the first link I was able to figure it out in a minute!

lst = {0, 1, 1, 1, 2, 2, 2, 6};
lst /. {x_?(# > 1 &) -> 1}
{0, 1, 1, 1, 1, 1, 1, 1}