Plotting with ggplot2: "Error: Discrete value supplied to continuous scale" on categorical y-axis

Question

The plotting code below gives Error: Discrete value supplied to continuous scale

What's wrong with this code? It works fine until I try to change the scale so the error is there... I tried to figure out solutions from similar problem but couldn't.

meltDF <- data.frame(
  MW = c(
    3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9,
    9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4,
    8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4,
    7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9,
    6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4,
    3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9,
    9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4, 8.1, 9, 9.4, 3.9, 6.4, 7.4,
    8.1, 9, 9.4
  ),
  variable = factor(
    c(
      "10", "10", "10", "10", "10", "10", "33.95", "33.95", "33.95",
      "33.95", "33.95", "33.95", "58.66", "58.66", "58.66", "58.66",
      "58.66", "58.66", "84.42", "84.42", "84.42", "84.42", "84.42",
      "84.42", "110.21", "110.21", "110.21", "110.21", "110.21", "110.21",
      "134.16", "134.16", "134.16", "134.16", "134.16", "134.16", "164.69",
      "164.69", "164.69", "164.69", "164.69", "164.69", "199.1", "199.1",
      "199.1", "199.1", "199.1", "199.1", "234.35", "234.35", "234.35",
      "234.35", "234.35", "234.35", "257.19", "257.19", "257.19", "257.19",
      "257.19", "257.19", "361.84", "361.84", "361.84", "361.84", "361.84",
      "361.84", "432.74", "432.74", "432.74", "432.74", "432.74", "432.74",
      "506.34", "506.34", "506.34", "506.34", "506.34", "506.34", "581.46",
      "581.46", "581.46", "581.46", "581.46", "581.46", "651.71", "651.71",
      "651.71", "651.71", "651.71", "651.71", "732.59", "732.59", "732.59",
      "732.59", "732.59", "732.59", "817.56", "817.56", "817.56", "817.56",
      "817.56", "817.56", "896.24", "896.24", "896.24", "896.24", "896.24",
      "896.24", "971.77", "971.77", "971.77", "971.77", "971.77", "971.77",
      "1038.91", "1038.91", "1038.91", "1038.91", "1038.91", "1038.91"
    ),
    levels = c(
      "10", "33.95", "58.66", "84.42", "110.21", "134.16", "164.69",
      "199.1", "234.35", "257.19", "361.84", "432.74", "506.34", "581.46",
      "651.71", "732.59", "817.56", "896.24", "971.77", "1038.91"
    )
  ),
  value = c(
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 1, 0, 0, 0, 0,
    0, 0, 0, 0, 0, 1, 1, 1, 0, 1, 0, 0, 0, 0, 0, 0
  )
)

The plotting code:

## Plotting
ggplot(meltDF[meltDF$value == 1,]) + geom_point(aes(x = MW, y = variable)) +
  scale_x_continuous(limits=c(0, 1200), breaks=c(0, 400, 800, 1200)) +
  scale_y_continuous(limits=c(0, 1200), breaks=c(0, 400, 800, 1200))

Here's how the plot looked before adding scale:

Plot

Your y values (variable) are factor, so you can't use scale_y_continuous. — Didzis Elferts
– Didzis Elferts, Commented Mar 26, 2015 at 12:21
Any quick solution how to change it into numeric or the one which is required ? Thanks! — Rechlay
– Rechlay, Commented Mar 26, 2015 at 12:23
Tried couple of solution but it doesn't work or I do it incorrectly. — Rechlay
– Rechlay, Commented Mar 26, 2015 at 13:29

smci · Accepted Answer · 2018-05-20 02:16:51Z

60

As mentioned in the comments, there cannot be a continuous scale on variable of the factor type. You could change the factor to numeric as follows, just after you define the meltDF variable.

meltDF$variable=as.numeric(levels(meltDF$variable))[meltDF$variable]

Then, execute the ggplot command

  ggplot(meltDF[meltDF$value == 1,]) + geom_point(aes(x = MW, y =   variable)) +
     scale_x_continuous(limits=c(0, 1200), breaks=c(0, 400, 800, 1200)) +
     scale_y_continuous(limits=c(0, 1200), breaks=c(0, 400, 800, 1200))

And you will have your chart.

Hope this helps

edited May 20, 2018 at 2:16

smci

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answered Mar 26, 2015 at 13:54

Nikos

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Comments

Kevin Arseneau · Accepted Answer · 2017-12-07 00:43:22Z

35

if x is numeric, then add scale_x_continuous(); if x is character/factor, then add scale_x_discrete(). This might solve your problem.

edited Dec 7, 2017 at 0:43

Kevin Arseneau

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answered Dec 6, 2017 at 21:19

yc_hello

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Comments

Mitoxys · Accepted Answer · 2018-03-26 09:54:33Z

8

In my case, you need to convert the column(you think this column is numeric, but actually not) to numeric

geom_segment(data=tmpp, 
   aes(x=start_pos, 
   y=lib.complexity, 
   xend=end_pos, 
   yend=lib.complexity)
)
# to 
geom_segment(data=tmpp, 
   aes(x=as.numeric(start_pos), 
   y=as.numeric(lib.complexity), 
   xend=as.numeric(end_pos), 
   yend=as.numeric(lib.complexity))
)

answered Mar 26, 2018 at 9:54

Mitoxys

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