Importing a txt file when number of columns varies?

I have problems importing a .txt file into R because the number columns changes from eight to nine. In开发者_如何学JAVAitially, my data has eight columns:

Date, Open, High, Low, Close, Volume, Open Interest, Delivery Month

Later, I add an additional column Unadjusted close. How should I import the data? Somehow the Unadjusted close column has to be ignored at the beginning. I've tried

data1 <- read.table("AD_0.TXT", sep=",", header=TRUE)

but that doesn't work.

You need to use the fill argument in the read.table function. Suppose I have the following file

"A","B","C"
1,2,3
4,5
6,7,8

called tmp.txt. Note that row two has only two values. Then

> a = read.table("tmp.txt", sep=",", header=TRUE, fill=TRUE)
> a
  A B  C 
1 1 2  3
2 4 5 NA
3 6 7  8

You use then standard sub-setting commands to remove (if you want to), any rows that contain NA:

> a[!is.na(a$C),]
  A B  C 
1 1 2  3
3 6 7  8