[R] create new

[Val]

Hi all,


I have several variables in a group and one group  contains three
variables. Sample of data ( Year, x1, x3 and x2)

mydat <- read.table(header=TRUE, text=' Year  x1  x3  x2
Year1  10  12    0
Year2   0  15    0
Year3   0   0    20
Year4  25   0   12
Year5  15  25   12
Year6   0  16   14
Year7   0  10    0')

I want create another variable( x4) based on the following condition.

if x1  > 0  then x4 = x1; regardless of  x2 and x3 values.
if x1  = 0  and x2  > 0 then x4 = x2;
if x1  = 0 and  x2  = 0 then x4 = x3

The desired output looks like as follows
Year    x1  x3  x2   x4
Year1  10  12    0  10
Year2    0  15    0  15
Year3    0    0   20  20
Year4  25    0   12  25
Year5  15  25   12  15
Year6    0  16   14  14
Year7    0  10     0  10

Thank you in advance