[R] How to calculate row means while ignore NAs

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Hi R users,

I have the dataframe as below:

w=c(5,6,7,8)
x=c(1,2,3,4)
y=c(1,2,3)
length(y)=4
z=data.frame(w,x,y)

z$mean1 <- rowMeans(subset(z, select = c(x, y)), na.rm = T)
z$mean2 <- rowMeans(subset(z, select = c(x, y)), na.rm=F)

  w x  y mean1 mean2
1 5 1  1     1     1
2 6 2  2     2     2
3 7 3  3     3     3
4 8 4 NA     4    NA

How to calculate mean value for the three columns, while default removing
NAs.
For example, for the fourth row, the mean value should be (8+4)/2 = 6

Thanks for your help.

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