I'm trying to add_trace ad each loop, but I get only one plot with multiplies lines on over each other.
mean <- -0.0007200342 sd <- 0.3403711 N=10 T=1 Delta = T/N W = c(0,cumsum( sqrt(Delta) * rnorm(N, mean=mean, sd=sd))) t <- seq(0,T, length=N+1) p<-plot_ly(y=W, x=t) for(i in 1:5){ W <- c(0,cumsum( sqrt(Delta) * rnorm(N, mean=mean, sd=sd))) p<-add_trace(p, y=W) } print(p) 
The plot_ly and add_trace functions have an evaluation = FALSE option that you can change to TRUE, which should fix the scope issues.
Use evaluate = TRUE in add_trace.
Nasty, but works:
mean <- -0.0007200342 sd <- 0.3403711 N=10 T=1 Delta = T/N W = c(0,cumsum( sqrt(Delta) * rnorm(N, mean=mean, sd=sd))) t <- seq(0,T, length=N+1) for(i in 1:5){ W <- c(0,cumsum( sqrt(Delta) * rnorm(N, mean=mean, sd=sd))) assign(paste("W_",i,sep=""),W) assign(paste("Name_", i, sep=""), paste("Name",i,sep="")) if(i==1){ pString<-"p<-plot_ly(x = t, y = W_1, name='W1')" } else { pString<-paste(pString, " %>% add_trace(x=t, y =", eval(paste("W", i, sep="_")),", name=", eval(paste("Name", i, sep="_")), ")", sep="") } } eval(parse(text=pString)) print(p) I'd do this like this:
mean <- -0.0007200342 sd <- 0.3403711 N=10 T=1 Delta = T/N # a list with the trace Y values Ws <- lapply( 1:15, function(idx){ c(0,cumsum( sqrt(Delta) * rnorm(N, mean=mean, sd=sd))) } ) # this could be a list with the trace X values, but is just a seq t <- seq(0,T, length=N+1) # a list with plotly compliant formatted objects formattedW <- lapply( seq_along(Ws), function(idx, datasetY, datasetX){ return(list( x = datasetX, y = datasetY[[idx]], type="scatter", mode = 'lines+markers')) }, datasetX = t, datasetY = Ws ) # Reduce the list of plotly compliant objs, starting with the plot_ly() value and adding the `add_trace` at the following iterations Reduce( function(acc, curr){ do.call(add_trace,c(list(p=acc),curr)) }, formattedW, init=plot_ly() ) It is described here : http://www.r-graph-gallery.com/129-use-a-loop-to-add-trace-with-plotly/
save your plot in a variable, and then do add_trace :
p <- plotly(...) p<- add_trace(p, ...)