I have a text file with a set of replacement rules, of the form
x^3y^2 -> 4, xy^2 -> 2, ...
for example. I'm having some issues trying to figure out how to tell Mathematica to read those rules and apply them. So far I've tried
F[x,y] /. "!cat rules.txt"
but that gave an invalid syntax error. Any suggestions?
EDIT
After some initial suggestions, here is some extra information:
After using the Import command as suggested by rm -rf, and removing the last comma from the text file, mathematica does not interpret the result as a list of replacement rules.
If I now do
replaceList = {Import["rules.txt"]};
F[x3,x4,x5] /. replaceList
Mathematica now says:
ReplaceAll::reps: {x5^3->5,
x4*x5^2->5,
x3*x5^2->5,
x2*x5^2->5} is neither a list of replacement rules nor a valid dispatch table, and so cannot be used for replacing. >>
EDIT2
Ok all, here is a very concrete example of what I'm facing. Thank you for helping me thus far, I'm sorry to be vague. In a text file called rules.txt I have the following content:
$ cat rules.text
x1*x2^2->1,
x1^2*x3->3,
x1^3->4
In mathematica I have the following code followed with an error:
F[x1_, x2_, x3_] := x1 *x2^2 + x1^2*x3 + x1^3
rules = Import["rules.text"]
{{"x1*x2^2->1,"}, {"x1^2*x3->3,"}, {"x1^3->4"}}
Obviously the formatting of the rules are incorrect, but if we try to brute force it, we get the error:
F[x1, x2, x3] /. rules
ReplaceAll::reps: {x1*x2^2->1,} is neither a list of replacement rules nor a valid dispatch table, and so cannot be used for replacing. >>
...
(*followed by similar errors for the other replacement rules read in*)
One quick attempt at fixing is to flatten the import table, or do what Michael E2 suggested:
rules = Flatten[Import["rules.text"]]
out = {"x1*x2^2->1,", "x1^2*x3,", "x1^3->4"}
F[x1, x2, x3] /. rules
ReplaceAll::reps:
"\!\({\"x1*x2^2->1,\", \"x1^2*x3->3,\", \"x1^3->4\"}\) is neither a list \
of replacement rules nor a valid dispatch.."
Or,
rules = ToExpression@Import["rules.text"]
ToExpression::sntx: Invalid syntax in or before "x1*x2^2->1, ".
ToExpression::sntx: Invalid syntax in or before "x1^2*x3->3, ".
Which fails also. Please let me know if I can add any more information to make the issue clearer, and thanks again.
EDIT3
I found a workaround solution. If one removes the comma from the text file, so that it reads:
$ cat rules.dat
x1*x2^2->1
x1^2*x3->3
x1^3->4
the following commands resolve the issue:
F[x1_, x2_, x3_] := x1 *x2^2 + x1^2*x3 + x1^3
F[x1, x2, x3] /. ToExpression@Flatten[Import["rules.dat"]]
out = 8
note the importance of the .dat extension. .txt does not work.
"!cat rules.txt"
would do what you wanted it to do? Have you looked atImport
? $\endgroup$