Plotting two variables as lines using ggplot2 on the same graph

Question

A very newbish question  but say I have data like this   test data  lt -   data frame      var0   100   c 0  cumsum runif 49  -20  20         var1   150   c 0  cumsum runif 49  -10  10         date   seq as Date  2002-01-01    by  1 month   length out 100        How can I plot both time series var0 and var1 on the same graph  with date on the x-axis  using ggplot2   Bonus points if you make var0 and var1 different colours  and can include a legend   I m sure this is very simple  but I can t find any examples out there

User · Answer

You need the data to be in  tall  format instead of  wide  for ggplot2   wide  means having an observation per row with each variable as a different column  like you have now   You need to convert it to a  tall  format where you have a column that tells you the name of the variable and another column that tells you the value of the variable  The process of passing from wide to tall is usually called  melting   You can use tidyr  gather to melt your data frame   library ggplot2  library tidyr   test data  lt -   data frame      var0   100   c 0  cumsum runif 49  -20  20         var1   150   c 0  cumsum runif 49  -10  10         date   seq as Date  2002-01-01    by  1 month   length out 100      test data   gt       gather key value  var0  var1    gt       ggplot aes x date  y value  colour key         geom line       Just to be clear the data that ggplot is consuming after piping it via gather looks like this    date        key     value 2002-01-01  var0    100 00000 2002-02-01  var0    115 16388      2007-11-01  var1    114 86302 2007-12-01  var1    119 30996

User · Answer

For a small number of variables  you can build the plot manually yourself   ggplot test data  aes date        geom line aes y   var0  colour    var0         geom line aes y   var1  colour    var1

User · Answer

Using your data   test data  lt - data frame  var0   100   c 0  cumsum runif 49  -20  20     var1   150   c 0  cumsum runif 49  -10  10     Dates   seq Date as Date  2002-01-01    by  1 month   length out 100     I create a stacked version which is what ggplot   would like to work with   stacked  lt - with test data                  data frame value   c var0  var1                              variable   factor rep c  Var0   Var1                                                     each   NROW test data                                Dates   rep Dates  2      In this case producing stacked was quite easy as we only had to do a couple of manipulations  but reshape   and the reshape and reshape2 might be useful if you have a more complex real data set to manipulate   Once the data are in this stacked form  it only requires a simple ggplot   call to produce the plot you wanted with all the extras  one reason why higher-level plotting packages like lattice and ggplot2 are so useful    require ggplot2  p  lt - ggplot stacked  aes Dates  value  colour   variable   p   geom line     I ll leave it to you to tidy up the axis labels  legend title etc   HTH

User · Answer

The general approach is to convert the data to long format  using melt   from package reshape or reshape2  or gather   pivot longer   from the tidyr package   library  reshape2   library  ggplot2    test data long  lt - melt test data  id  date      convert to long format  ggplot data test data long         aes x date  y value  colour variable            geom line       Also see this question on reshaping data from wide to long

User · Answer

I am also new to R but trying to understand how ggplot works I think I get another way to do it  I just share probably not as a complete perfect solution but to add some different points of view    I know ggplot is made to work with dataframes better but maybe it can be also sometimes useful to know that you can directly plot two vectors without using a dataframe   Loading data  Original date vector length is 100 while var0 and var1 have length 50 so I only plot the available data  first 50 dates    var0  lt - 100   c 0  cumsum runif 49  -20  20    var1  lt - 150   c 0  cumsum runif 49  -10  10    date  lt - seq as Date  2002-01-01    by  1 month   length out 50        Plotting  ggplot     geom line aes x date y var0  color  red                 geom line aes x date y var1  color  blue                 ylab  Values   xlab  date       However I was not able to add a correct legend using this format  Does anyone know how

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