Referencing x axis variable from a melted data frame to plot using ggplot2 in R

Question

I have a data frame df with 10 columns such as this,

row.names   c(300, 400, 500, 600, 700)  X1  X2  X3  X4  X5  X6  X7  X8  X9
1   absTLM_3_4  300 -4.147782e-08   -3.360635e-08   -3.306786e-08   -3.133482e-08   -3.124207e-08   -3.056317e-08   -3.020253e-08   -2.950814e-08   -2.955155e-08
2   absTLM_4_5  400 -3.703708e-08   -3.013687e-08   -2.746570e-08   -2.627163e-08   -2.528328e-08   -2.457543e-08   -2.437666e-08   -2.412295e-08   -2.358447e-08
3   absTLM_5_6  500 -3.575756e-08   -2.694028e-08   -2.457341e-08   -2.331162e-08   -2.262283e-08   -2.180886e-08   -2.104917e-08   -2.101946e-08   -2.081650e-08
4   absTLM_6_7  600 -2.454283e-08   -2.152165e-08   -1.967477e-08   -1.885213e-08   -1.835989e-08   -1.814608e-08   -1.806438e-08   -1.785795e-08   -1.784158e-08
5   absTLM_7_8  700 -2.317125e-10   -1.029456e-08   -1.076342e-08   -1.365264e-08   -1.378578e-08   -1.457421e-08   -1.463740e-08   -1.480280e-08   -1.515121e-0

Now I would like to plot column 1 in the x-axis versus columns 2,5,6, and 8 in the y-axis. For doing this I use the following piece of code,

x4 <- melt(df, id=names(df)[1], measure=names(df)[c(2, 5, 6, 8)], variable = "cols")
plt <- ggplot(x4) +
        geom_line(aes(x=x,y= value, color=cols), size=1) +
        labs(x = "x", y = "y")

When I call the plot object plt I get an Error in eval(expr, envir, enclos) : object 'x' not found.
Could someone kindly point out what I should change here to display the plot correctly.

Thanks.

There's no column named x in X4. See head(x4) and adjust your geom_line(aes()) accordingly. — Brandon Bertelsen
– Brandon Bertelsen, Commented Jan 24, 2014 at 11:21
@BrandonBertelsen it seems column header of the first column which I need is named c(300, 400, 500, 600, 700) , now when I use plt <- ggplot(x4) + geom_line(aes(x=c(300, 400, 500, 600, 700),y= value, color=cols), size=1) + labs(x = "x", y = "y") I still get an error such as, Aesthetics must either be length one, or the same length as the dataProblems:c(300, 400, 500, 600, 700) — Amm
– Amm, Commented Jan 24, 2014 at 12:32
I think you should just rename the columns and use a typical style (no space in column names only _ or .). colnames(df)[1] <- "x" and perhaps your original code will work. Could you provide us with dput(head(df))? — Brandon Bertelsen
– Brandon Bertelsen, Commented Jan 24, 2014 at 13:01

Brandon Bertelsen · Accepted Answer · 2014-01-24 13:32:15Z

1

It looks like your column names are buggered. Try this:

x4 <- melt(df, id=names(df)[1], measure=names(df)[c(2, 5, 6, 8)], variable = "cols")
colnames(x4)[1] <- "x"
plt <- ggplot(x4) +
        geom_line(aes(x=x,y= value, color=cols), size=1) +
        labs(x = "x", y = "y")

edited Jan 24, 2014 at 13:32

answered Jan 24, 2014 at 13:10

Brandon Bertelsen

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1 Comment

Amm Over a year ago

Yes, you were right. After changing the column header name it works! Thanks for your useful suggestions.

Amm · Accepted Answer · 2014-01-24 14:19:22Z

The reason why the following piece of code did not correctly plot the data was due to the column header name c(300, 400, 500, 600, 700) which was name of the first column in the data frame df.

x4 <- melt(df, id=names(df)[1], measure=names(df)[c(2, 5, 6, 8)], variable = "cols")
plt <- ggplot(x4) +
        geom_line(aes(x=x,y= value, color=cols), size=1) +
        labs(x = "x", y = "y")

So the column header name of df had to be changed first, according to the suggestion by Brandon Bertelsen, the column header name of c(300, 400, 500, 600, 700) was changed to x by the following line of code,

colnames(df)[1] <- "x"

Once the column header name is changed, then the data frame can be melted after which the plotting works correctly,

x4 <- melt(df, id=names(df)[1], measure=names(df)[c(2, 5, 6, 8)], variable = "cols")
plt <- ggplot(x4) +
        geom_point(aes(x=x,y= value, color=cols), size=2) +
        labs(x = "x", y = "y")

So the plot plt looks like this,

enter image description here

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