Hassan, Others have provided you with better solutions, but I hope this allows you to see why yours didn't work.
# first (going with your code) you needed a data.frame called "x" # here is an example: x <- structure(list(x1 = c(0.0986048226696643, -0.445652024980979, 0.0893989676314604, -3.02656448303247, -0.966125836458264, -1.49916656636977, -1.43173455089552, 0.370528111260298, -1.16980816517156, -0.808744946153693 ), x2 = c(-0.765406771195136, -0.37933377428095, 1.38846324586498, -1.70043724374807, -0.71331175577977, 1.44597103991061, 1.31674350467787, -0.954578441470943, -1.30637013925954, 0.551870274117374), x3 = c(-0.122350075070145, 1.6217818199546, -0.824570718637696, -0.0341988842898353, 1.03924814479596, 0.898533448980663, 0.68074228601446, 0.296251937506574, -0.698501590358135, -0.0533564535030227)), .Names = c("x1", "x2", "x3"), row.names = c(NA, -10L), class = "data.frame") # you then need an empty vector to hold the results of your for loop (called "z" here) # note the square brackets as opposed to your parentheses z <- vector("list") for (i in 1:ncol(x)) { z[i] = 200 - x[i] } # finally, this will reassemble the output of the for loop z <- do.call(cbind, z) colnames(z) <- c("z1", "z2", "z3") # Finally, do read what the others sent you as they provide more efficient solutions HTH Chuck Hassan Eini Zinab wrote > > Dear All, > > I have a data set with variables x1, x2, x3, ..., x20 and I want to > create z1, z2, z3, ..., z20 with the following formula: > > > z1 = 200 - x1 > z2 = 200 - x2 > z3 = 200 - x3 > . > . > . > z20 = 200 - x20. > > > I tried using a for loop and its index as: > > for (i in 1:20) { > z(i) = 200 - x(i) > } > > But R gives the following error message: "Error: could not find function > "x"". > > Is there any other way for a simple coding of my 20 lines of code? > > Alohas, > Hassan Eini-Zinab > > ______________________________________________ > R-help@ mailing list > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. > -- View this message in context: http://r.789695.n4.nabble.com/For-loop-and-using-its-index-tp4459454p4460277.html Sent from the R help mailing list archive at Nabble.com. ______________________________________________ R-help@r-project.org mailing list https://stat.ethz.ch/mailman/listinfo/r-help PLEASE do read the posting guide http://www.R-project.org/posting-guide.html and provide commented, minimal, self-contained, reproducible code.