Cannot add traces in a loop

[aljabadi]

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Hi,

I'm just wondering why the following plots turn out differently (I only change 3 numbers to a variable containing them (i). Even when I run the code lines one after another.
Interestingly, if I use different variable names (i,j,k, etc), I get the expected result.

library(plotly)

#### Code 1
df <- data.frame(a1=seq(1,20), a2=seq(21,40), a3=seq(41,60))
p <- df %>% plot_ly(x = ~seq(1,dim(df)[1]))
i=1
p <- p %>% add_trace(y = ~ df[,paste0('a',1)]) 
i=2
p <- p %>% add_trace(y = ~ df[,paste0('a',2)])
i=3
p <- p %>% add_trace(y = ~ df[,paste0('a',3)])
p

#### Code 2
df <- data.frame(a1=seq(1,20), a2=seq(21,40), a3=seq(41,60))
p <- df %>% plot_ly(x = ~seq(1,dim(df)[1]))
i=1
p <- p %>% add_trace(y = ~ df[,paste0('a',i)]) 
i=2
p <- p %>% add_trace(y = ~ df[,paste0('a',i)])
i=3
p <- p %>% add_trace(y = ~ df[,paste0('a',i)])
p

[aljabadi]

duplicate of https://stackoverflow.com/questions/34186560/plotly-add-trace-in-a-loop