how to read a file line by line in D

On Thursday, 6 September 2018 at 16:13:42 UTC, hridyansh thakur wrote:
> how to read a file line by line in D

std.stdio.File.byLine()

Refer the doc here: https://dlang.org/library/std/stdio/file.by_line.html

An example from the doc:

```
import std.algorithm, std.stdio, std.string;
// Count words in a file using ranges.
void main()
{
    auto file = File("file.txt"); // Open for reading
    const wordCount = file.byLine()            // Read lines
                          .map!split           // Split into words
                          .map!(a => a.length) // Count words per line
                          .sum();              // Total word count
    writeln(wordCount);
}
```

On 07/09/2018 4:17 AM, Arun Chandrasekaran wrote:
> On Thursday, 6 September 2018 at 16:13:42 UTC, hridyansh thakur wrote:
>> how to read a file line by line in D
> 
> std.stdio.File.byLine()
> 
> Refer the doc here: https://dlang.org/library/std/stdio/file.by_line.html
> 
> An example from the doc:
> 
> ```
> import std.algorithm, std.stdio, std.string;
> // Count words in a file using ranges.
> void main()
> {
>      auto file = File("file.txt"); // Open for reading
>      const wordCount = file.byLine()            // Read lines
>                            .map!split           // Split into words
>                            .map!(a => a.length) // Count words per line
>                            .sum();              // Total word count
>      writeln(wordCount);
> }
> ```

Ranges will be far too advanced of a topic to bring up at this stage.

So something a little more conventional might be a better option:

---
import std.file : readText;
import std.array : split;
import std.string : strip;

string text = readText("file.txt");
string[] onlyWords = text.split(" ");

uint countWords;
foreach(ref word; onlyWords) {
	word = word.strip();
	if (word.length > 0)
		countWords++;
}
---

On 9/6/18 1:07 PM, rikki cattermole wrote:
> On 07/09/2018 4:17 AM, Arun Chandrasekaran wrote:
>> On Thursday, 6 September 2018 at 16:13:42 UTC, hridyansh thakur wrote:
>>> how to read a file line by line in D
>>
>> std.stdio.File.byLine()
>>
>> Refer the doc here: https://dlang.org/library/std/stdio/file.by_line.html
>>
>> An example from the doc:
>>
>> ```
>> import std.algorithm, std.stdio, std.string;
>> // Count words in a file using ranges.
>> void main()
>> {
>>      auto file = File("file.txt"); // Open for reading
>>      const wordCount = file.byLine()            // Read lines
>>                            .map!split           // Split into words
>>                            .map!(a => a.length) // Count words per line
>>                            .sum();              // Total word count
>>      writeln(wordCount);
>> }
>> ```
> 
> Ranges will be far too advanced of a topic to bring up at this stage.
> 
> So something a little more conventional might be a better option:
> 
> ---
> import std.file : readText;
> import std.array : split;
> import std.string : strip;
> 
> string text = readText("file.txt");
> string[] onlyWords = text.split(" ");
> 
> uint countWords;
> foreach(ref word; onlyWords) {
>      word = word.strip();
>      if (word.length > 0)
>          countWords++;
> }
> ---

Ugh, don't do that, it will read the unknown-length file into RAM all at once.

foreach(word; File("file.txt").byLine)
{
   word = word.strip();
   if(word.length > 0) countWords++;
}

That will buffer one line at a time and achieve the same results.

-Steve

On 9/6/18 2:30 PM, Steven Schveighoffer wrote:
> On 9/6/18 1:07 PM, rikki cattermole wrote:
>> On 07/09/2018 4:17 AM, Arun Chandrasekaran wrote:
>>> On Thursday, 6 September 2018 at 16:13:42 UTC, hridyansh thakur wrote:
>>>> how to read a file line by line in D
>>>
>>> std.stdio.File.byLine()
>>>
>>> Refer the doc here: https://dlang.org/library/std/stdio/file.by_line.html
>>>
>>> An example from the doc:
>>>
>>> ```
>>> import std.algorithm, std.stdio, std.string;
>>> // Count words in a file using ranges.
>>> void main()
>>> {
>>>      auto file = File("file.txt"); // Open for reading
>>>      const wordCount = file.byLine()            // Read lines
>>>                            .map!split           // Split into words
>>>                            .map!(a => a.length) // Count words per line
>>>                            .sum();              // Total word count
>>>      writeln(wordCount);
>>> }
>>> ```
>>
>> Ranges will be far too advanced of a topic to bring up at this stage.
>>
>> So something a little more conventional might be a better option:
>>
>> ---
>> import std.file : readText;
>> import std.array : split;
>> import std.string : strip;
>>
>> string text = readText("file.txt");
>> string[] onlyWords = text.split(" ");
>>
>> uint countWords;
>> foreach(ref word; onlyWords) {
>>      word = word.strip();
>>      if (word.length > 0)
>>          countWords++;
>> }
>> ---
> 
> Ugh, don't do that, it will read the unknown-length file into RAM all at once.
> 
> foreach(word; File("file.txt").byLine)
> {
>     word = word.strip();
>     if(word.length > 0) countWords++;
> }
> 
> That will buffer one line at a time and achieve the same results.

ugh, I didn't think this through. This works:

foreach(line; File("file.txt").byLine)
{
   foreach(word; line.split(" "))
   {
   	word = word.strip();
   	if(word.length > 0) countWords++;
   }
}

-Steve