Add columns of dataset

mydf = data.frame(id=1:3,var1=c(0,.4,0),var2=c(.1,.6,0),var4=c(.3,0,0),var7=c(.9,0,.8),var8=c(0,.2,.7))
allvars = c('id',paste('var',1:8,sep=''))
mydf[,allvars[!allvars %in% names(mydf)]] = 0
mydf = mydf[,sort(names(mydf))]
mydf

Dear all,

I have a dataset that looks like

id  var1  var2  var4  var7  var8
1    0.0   0.1    0.3    0.9    0.0
2    0.4   0.6    0.0    0.0    0.2
3    0.0   0.0    0.0    0.8    0.7

Some columns are missed, for example, here the fourth (var3), sixth(var5)
and seventh (var6) columns. I want to first determine which columns are
missed in a huge dataset and then add the missed columns with the values of
zeros that looks like

id  var1  var2   var3  var4  var5  var6  var7  var8
1    0.0   0.1     0.0    0.3   0.0    0.0   0.9    0.0
2    0.4   0.6     0.0    0.0   0.0    0.0   0.0    0.2
3    0.0   0.0     0.0    0.0   0.0    0.0   0.8    0.7

Can anybody please help how to get this done? Thanks a lot in advance

Lisa

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