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From the r-help mailing list:

x <- rnorm(10)
y <- runif(10)
z <- 1:10

plot(x~z, ylim=range(x, y), type='l')
lines(y, col='red')

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If you're not happy with what R puts on the axes of your plot (tickmarks, labels etc), plot with "axes=F", then add custom axes with the "axis()" function.

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You have a plot, and you want to draw a grid behind it. If you add the grid to the plot, using either

grid()

or

abline()

, the lines will be added on top of your plot, not behind it. I found the solution on the R-help mailing list, here. Redraw the plot after adding the grid, but first set

par(new=T)

so that it will be drawn on top of the old plot on the same device.

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To replace all NA values in an object with zeroes:

x[is.na(x)] <- 0

If you want to do this only for some columns in a matrix or data frame, try this tip, which was posted by John Fox on the R-help mailing list:

cols <- c(1,3)
x[,cols][is.na(x[,cols])] <- 0

If you want to replace the NAs everywhere except in a single column, spare yourself some typing by:

cols <- -3

(then,

x[,cols][is.na(x[,cols])] <- 0

replaces everywhere except in the third column.)

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x is your data frame. x$total is the column you want to remove:

x$total <- NULL

More at the R Wiki