Is there an fread analog for reading from stdin?

Question

I'd like to use fread in a (R)script that would get input data via the linux pipe mechanism. Is there an fread analog for the following?

read.csv(file = 'stdin', ...)

I'll also settle for reading stdin some other way and then using fread to parse it, as I mainly want this for fread's superior separator and header logic.

Answer 1

Turns out it's as simple as:

fread('file:///dev/stdin')

This works, because fread actually creates a temporary file when the first 7 characters are "file://" or "http://" and uses download.file to copy the data there and then fread that.

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Update: As of version 1.8.11 one can use shell commands in fread, making another solution possible:

fread('cat /dev/stdin')

Answer 2

All of the read.* functions use 'scan' under their hoods. scan is fairly low level but does have the capacity for parsing lines of data into different classes.

> mat <- matrix(scan(), 4,4) # will paste in block of data 
1: 0.5 0.1428571 0.25
4: 0.5 0.1428571 0.25
7: 0.5 0.1428571 0.25
10: 0.5 0.1428571 0.25
13: 0.5 0.1428571 0.25
16: 0.5 
17:        # Terminate with two <cr>'s
Read 16 items
> mat
          [,1]      [,2]      [,3]      [,4]
[1,] 0.5000000 0.1428571 0.2500000 0.5000000
[2,] 0.1428571 0.2500000 0.5000000 0.1428571
[3,] 0.2500000 0.5000000 0.1428571 0.2500000
[4,] 0.5000000 0.1428571 0.2500000 0.5000000


> lst <- scan(what=list(double(0), "a"))
1: 4 t
2: 6 h
3:  8 l
4: 8 8
5: 
Read 4 records
> lst
[[1]]
[1] 4 6 8 8

[[2]]
[1] "t" "h" "l" "8"

You should also look at the ?connections page.