Argthtjtr

first time asking question here so if I mess up something, please let me know I'll be happy to fix it.

While trying to dynamically create multiple graphs generated by ggplot2 and then print the graphs using gridExtra::grid.arrange, I noticed that using a for loop or using lapply produce different results.

Surprisingly, while lapply produces the expected result, the graphs created with the for loop end up with having all the same y data.

Here is a reproducible example:

library(ggplot2)

library(gridExtra)



gen.plot <- function(df, x.colName, y.colName, title,

                            movavg.period) {

  # print(y.colName)

  p <- ggplot(df, aes(x = df[[x.colName]],

                      y = df[[y.colName]])) +

    geom_line() +

    xlab("Time") +

    ylab("Value") +

    ggtitle(title)



  return(p)

}



titles <- c("down", "mid", "up")

df <- data.frame(tick = seq(0, 10, 1),

                 down = seq(2, 1, -0.1),

                 mid = rep(3, 11),

                 up = seq(5,6, 0.1))



plots.list <- list()

for(t in titles) {

  plots.list[[length(plots.list) + 1]] <- gen.plot(df, "tick", 

                                            t, t, 2)

}

grid.arrange(grobs = plots.list, nrow = 3)



plots.list <- lapply(titles, FUN =  function(t, lapply.df) {

  gen.plot(lapply.df, "tick", 

        t, t, 2)

}, lapply.df = df)



grid.arrange(grobs = plots.list, nrow = 3)

Now, where it becomes really weird, is that if you uncomment the print call in the function that prints out the y.colName variable, the for loop works as expected. But it only works if you print out this specific variable, not any of the other function variable. Also, as you can see in the code, the y.colName variable is used in the title of the graph, and the title is correct in every graph.

Also, I've tried taking the code out of the function but it provides the same results and the print call trick does not work anymore.

I can't post image without 10 reputation so links will have to do.

Here is what I get with the for loop:
forloop

Here is what I get with lapply:
lapply

Here is my sessionInfo():

R version 3.4.3 (2017-11-30)

Platform: x86_64-w64-mingw32/x64 (64-bit)

Running under: Windows 7 x64 (build 7601) Service Pack 1



Matrix products: default



locale:

[1] LC_COLLATE=English_Ireland.1252  LC_CTYPE=English_Ireland.1252   

[3] LC_MONETARY=English_Ireland.1252 LC_NUMERIC=C                    

[5] LC_TIME=English_Ireland.1252    



attached base packages:

  [1] stats     graphics  grDevices utils     datasets  methods   base     



other attached packages:

  [1] gridExtra_2.3 ggplot2_2.2.1



loaded via a namespace (and not attached):

[1] labeling_0.3     colorspace_1.3-2 scales_0.5.0     compiler_3.4.3  

[5] lazyeval_0.2.0   plyr_1.8.4       tools_3.4.3      pillar_1.2.1    

[9] gtable_0.2.0     tibble_1.4.2     yaml_2.1.14      Rcpp_0.12.16    

[13] grid_3.4.3       rlang_0.2.0      munsell_0.4.3 

Please, if you understand what's happening here, explain it to me, help me get my sleep back.

Try this:

gen.plot <- function(df, x.colName, y.colName, title,

                     movavg.period) {

  # print(y.colName)

  p <- ggplot(df, aes_string(x = x.colName,

                             y = y.colName)) +

    geom_line() +

    xlab("Time") +

    ylab("Value") +

    ggtitle(title)



  return(p)

}

It should give you consist and correct results whichever method you use to implement it (i.e., lapply or for loop). Using ggplot2 in this way allows you to specify the variable names using a string. And you should be specifying variable names and not giving aes the entire column from the data frame.