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I am melting a data frame in order to plot it in ggplot2. However, geom_line() is not giving me horizontal lines. Instead it is transforming my points to vertical lines. I will attach images and add the code to further illustrate:

Using only geom_point():

vecmmelt = melt(tail(tempdf,7), id.vars = "Date")

ggplot(vecmmelt, aes(x = Date, y = value, colour = variable, group=1)) +geom_point()+theme_bw()

Using geom point only

Now I would expect to have the following when using geom_line():

Expectation from + geom_line

What I am really getting by using the following code is the following picture:

vecmmelt = melt(tail(tempdf,7), id.vars = "Date")

ggplot(vecmmelt, aes(x = Date, y = value, colour = variable, group=1)) +geom_point()+geom_line()

Reality that is wrong

I tried using geom_path() and it also is wrong

Claus Wilke
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J.Doe
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2 Answers2

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It looks like the problem is that you are specifying group=1, which tells ggplot to connect all the dots. As Mario Barbé explained for a similar question:

For line graphs, the data points must be grouped so that it knows which points to connect. In this case, it is simple -- all points should be connected, so group=1. When more variables are used and multiple lines are drawn, the grouping for lines is usually done by variable.

Reference: Cookbook for R, Chapter: Graphs Bar_and_line_graphs_(ggplot2), Line graphs.

So, in your case, you should specify group=variable to fix the issue.

altabq
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This is not because of your variable grouping, but because your date format is not correct. Instead of it understanding it as d-M-Y, it is understanding it as M-d-Y, so you have many values for each months but not days in between. Try reformating your date: df$Date <-as.Date(paste(df$Year, df$Momnth, 01), "%Y %m %d")

choabf
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