Julia Language Input Reading Data from a File
Example
Reading strings or bytes
Files can be opened for reading using the open function, which is often used together with do block syntax:
open("myfile") do f
for (i, line) in enumerate(eachline(f))
print("Line $i: $line")
end
end
Suppose myfile exists and its contents are
What's in a name? That which we call a rose
By any other name would smell as sweet.
Then, this code would produce the following result:
Line 1: What's in a name? That which we call a rose
Line 2: By any other name would smell as sweet.
Note that eachline is a lazy iterable over the lines of the file. It is preferred to readlines for performance reasons.
Because do block syntax is just syntactic sugar for anonymous functions, we can pass named functions to open too:
julia> open(readstring, "myfile")
"What's in a name? That which we call a rose\nBy any other name would smell as sweet.\n"
julia> open(read, "myfile")
84-element Array{UInt8,1}:
0x57
0x68
0x61
0x74
0x27
0x73
0x20
0x69
0x6e
0x20
⋮
0x73
0x20
0x73
0x77
0x65
0x65
0x74
0x2e
0x0a
The functions read and readstring provide convenience methods that will open a file automatically:
julia> readstring("myfile")
"What's in a name? That which we call a rose\nBy any other name would smell as sweet.\n"
Reading structured data
Suppose we had a CSV file with the following contents, in a file named file.csv:
Make,Model,Price
Foo,2015A,8000
Foo,2015B,14000
Foo,2016A,10000
Foo,2016B,16000
Bar,2016Q,20000
Then we may use the readcsv function to read this data into a Matrix:
julia> readcsv("file.csv")
6×3 Array{Any,2}:
"Make" "Model" "Price"
"Foo" "2015A" 8000
"Foo" "2015B" 14000
"Foo" "2016A" 10000
"Foo" "2016B" 16000
"Bar" "2016Q" 20000
If the file were instead delimited with tabs, in a file named file.tsv, then the readdlm function can be used instead, with the delim argument set to '\t'. More advanced workloads should use the CSV.jl package.
