R color scatter plot points based on values

Question

I am able to plot a scatter plot and color the points based on one criteria  i e  I can color all points   3 as red and the remainder as black  I would love to be able to color points in this fashion        3 color red   lt  1 color blue  The rest as black   The code I have below completes step 1 and 3 but I am not sure how to incorporate the second argument of step 2  data lt - read table  sample data txtt   header TRUE  row name 1  pos lt - data col name1 cn lt - data col name2 plot pos cn  ylim c 0 5   col  blue   plot pos cn  col ifelse cn gt  3  red   black    ylim c 0 10     Any help would be great    Thanks in advance

User · Answer

It s better to create a new factor variable using cut    I ve added a few options using ggplot2 also   df  lt - data frame    X1 seq 0  5  by 0 001     X2 rnorm df X1  mean   3 5  sd   1 5       Create new variable for plotting df Colour  lt - cut df X2  breaks   c -Inf  1  3   Inf                     labels   c  low    medium    high                      right   FALSE       Base Graphics  plot df X1  df X2        col   df Colour  ylim   c 0  10   xlab    POS         ylab    CS   main    Plot Title   pch   21   plot df X1 df X2        col   df Colour  ylim   c 0  10   xlab    POS         ylab    CS   main    Plot Title   pch   19  cex   0 5     Using  with      with df        plot X1  X2  xlab  POS   ylab  CS   col   Colour  pch 21  cex 1 4            Using ggplot2 library ggplot2     qplot   qplot df X1  df X2  colour   df Colour     ggplot   p  lt - ggplot df  aes X1  X2  colour   Colour    p  lt - p   geom point     xlab  POS     ylab  CS   p  p   facet grid Colour    scales    free

User · Answer

Best thing to do here is to add a column to the data object to represent the point colour   Then update sections of it by filtering   data lt - read table  sample data txtt   header TRUE  row name 1    Create new column filled with default colour data Colour  black    Set new column values to appropriate colours data Colour data col name2 gt  3   red  data Colour data col name2 lt  1   blue    Plot all points at once  using newly generated colours plot data col name1 data col name2  ylim c 0 5   col data Colour  ylim c 0 10     It should be clear how to adapt this for plots with more colours  amp  conditions

User · Answer

Also it d work to just specify ifelse   twice   plot pos cn  col  ifelse cn  gt   3   red   ifelse cn  lt   1  blue    black     ylim   c 0  10

User · Answer

Here is a method using a lookup table of thresholds and associated colours to map the colours to the variable of interest          make a grid  Grd  of points and number points for side of square  GrdD  Grd  lt - expand grid seq 0 5 400 5 10  seq 0 5 400 5 10   GrdD  lt - length unique Grd Var1      Add z-values to the grid points Grd z  lt - rnorm length Grd Var1   mean   10  sd  2     Make a vector of thresholds  Brks  to colour code z  Brks  lt - c seq 0 18 3  Inf     Make a vector of labels  Lbls  for the colour threhsolds Lbls  lt - Lbls  lt - c  0-3   3-6   6-9   9-12   12-15   15-18    gt 18      Make a vector of colours  Clrs  for to match each range Clrs  lt - c  grey50   dodgerblue   forestgreen   orange   red   purple   magenta      Make up lookup dataframe  LkUp  of the lables and colours  LkUp  lt - data frame cbind Lbls Clrs  stringsAsFactors   FALSE     Add a new variable  Lbls  the grid dataframe mapping the labels based on z-value Grd Lbls  lt - as character cut Grd z  breaks   Brks  labels   Lbls      Add a new variable  Clrs  to the grid dataframe based on the Lbls field in the grid and lookup table Grd  lt - merge Grd LkUp  by x    Lbls      Plot the grid using the  Clrs  field for the colour of each point plot Grd Var1       Grd Var2       xlim   c 0 400        ylim   c 0 400        cex   1 0       col   Grd Clrs       pch   20       xlab    mX        ylab    mY        main    My Grid        axes   FALSE       labels   FALSE       las   1    axis 1 seq 0 400 100   axis 2 seq 0 400 100  las   1  box col    black    legend  topleft   legend   Lbls  fill   Clrs  title    Z

[r] R color scatter plot points based on values

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