how to apply a rule involving a hundred variables in mathematica

问题

I have an expression which involves x1,x2,...,x100, I also have a list lst with 100 elements, how to apply the rule to this expression to achieve something like the following:

exp/.{x1->lst[[1]],x2->lst[[2]],...,x100->lst[[100]]}

Thanks!

回答1:

 exp /.  Table[Symbol["x" <> ToString[i]] -> lst[[i]], {i, 1, 100}]  

So you don't need to write X1,X2, ... X100

回答2:

You can use Thread to apply the rules to each pair of expressions:

Thread[{a, b, c} -> {1, 2, 3}]

回答3:

It is much simpler and more convenient to solve such tasks using indexed variables instead of generation of a list of different Symbols. In this way:

listOfRules = Array[f@# :> list[[#]] &, {100}];
Short@%

=> {f[1]:>list[[1]],f[2]:>list[[2]],f[3]:>list[[3]],f[4]:>list[[4]],
<<92>>,f[97]:>list[[97]],f[98]:>list[[98]],f[99]:>list[[99]],f[100]:>list[[100]]}

If you plan to make such replacement many times, it is worth to Dispatch large list of rules:

listOfRules = Dispatch@listOfRules;

The replacement can be made as usual:

expr /. listOfRules

来源：https://stackoverflow.com/questions/4743121/how-to-apply-a-rule-involving-a-hundred-variables-in-mathematica