Thank you, this works very well. My only remaining question about this is about how ifelse is working; I understand the basic syntax (df$condition2 gets assigned the value *runif(nrow(df1[df1$condition1<=1,]),0,1)* or the value *df$condition1* depending on whether or not df$condition1 meets the criterion "<=1".
As I understand it, "runif(nrow(df1[df1$condition1<=1,]),0,1)" is a vector of random values with vector length equal to the number of rows meeting "df$condition1<=1" and df$condition1 is just my column of condition1 values. So the command seems to be going down row by row and assigning condition2 values from one of two vectors in an "interleaved" way. So my question is, how does R keep track of which item in each of the vectors to assign to condition2? For example, if the first 4 entries of condition1 are 1, 3, 4, 1, how does R know to use the *first* entry of vector runif(nrow(df1[df1$condition1<=1,]),0,1) then the *second* and *third* values of vector df$condition1, then the *second* value of vector runif(nrow(df1[df1$condition1<=1,]),0,1)? -- View this message in context: http://r.789695.n4.nabble.com/Performing-operations-only-on-selected-data-tp4650646p4650803.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.
