Import data into R with an unknown number of columns?

Question

I\'m trying to read a text file with different row lengths:

1
1   2
1   2   3
1   2   3   4
1   2   3   4   5
1   2   3   4   5   6
1   2   3   4   5   6   7         


        

Answer 1

Using count.fields is definitely the right approach for this, but just for completeness:

Another option is to bring in all the raw text and parse it within R:

x <- readLines(textConnection(
"1\t
1\t2
1\t2\t3
1\t2\t3\t4
1\t2\t3\t4\t5
1\t2\t3\t4\t5\t6"))
x <- strsplit(x,"\t")

To combine a list of unequal length vectors, the easiest approach is to use the rbind.fill function from plyr:

library(plyr)
# requires data.frames with column names
x <- lapply(x,function(x) {x <- as.data.frame(t(x)); colnames(x)=1:length(x); return(x)})
do.call(rbind.fill,x)
1    2    3    4    5    6
1 1 <NA> <NA> <NA> <NA> <NA>
2 1    2 <NA> <NA> <NA> <NA>
3 1    2    3 <NA> <NA> <NA>
4 1    2    3    4 <NA> <NA>
5 1    2    3    4    5 <NA>
6 1    2    3    4    5    6

Answer 2

There is nice function count.fields (see help) which counts number of column per row:

count.fields("test", sep = "\t")
#[1] 1 2 3 4 5 6 7 8

So, using your second solution:

no_col <- max(count.fields("test", sep = "\t"))
data <- read.table("test",sep="\t",fill=TRUE,col.names=1:no_col)
data
#   X1 X2 X3 X4 X5 X6 X7 X8
# 1  1 NA NA NA NA NA NA NA
# 2  1  2 NA NA NA NA NA NA
# 3  1  2  3 NA NA NA NA NA
# 4  1  2  3  4 NA NA NA NA
# 5  1  2  3  4  5 NA NA NA
# 6  1  2  3  4  5  6 NA NA
# 7  1  2  3  4  5  6  7 NA
# 8  1  2  3  4  5  6  7  8