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Shell Programming and Scripting

AWK quiz, multiple choice

View Poll Results: What does that awk code do with the awk manual page?
The word frequencies, with words grouped by frequency, in descending order. 8 88.89%
Same word average distances (i.e. how many chars in between two same words), with words grouped by avg distance, in descending order. 1 11.11%
The average positions in which a word appears inside a sentence, with words grouped by average position, in descending order. 0 0%
Voters: 9. This poll is closed

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Top Forums Shell Programming and Scripting AWK quiz, multiple choice
# 1  
Old 05-25-2009
AWK quiz, multiple choice
Nobody cared about the original post, or perhaps it was a bit difficult to guess.
Therefore I am including a poll here.

Code:
nawk -F'[^A-Za-z_]+' '
{i=NF;for(;i;i--)if($i)w[tolower($i)]++}
END{
  for(k in w){c=w[k];x[c]=x[c]k",";if(c>m)m=c}
  for(;m;m--)if(m in x)print m,x[m]
  }
' <(man nawk)

# 2  
Old 05-25-2009
Voted for the second option.
I would write it like this:

Code:
nawk -F'[^A-Za-z_]+' '{
  for (i=1; i<=NF; i++) 
    $i && w[tolower($i)]++
    }
END{
  for (k in w) {
    c = w[k]
    x[c] = c in x ? x[c] "," k : k
    (c > m) && m = c
    }
  do 
    if (m in x) print m, x[m] 
      while (m--) 
  }' <(man nawk)

# 3  
Old 05-25-2009
Quote:
Originally Posted by radoulov
Voted for the second option.
I would write it like this:
I like your style, you saved a few characters.

This one tough
Code:
for (i=1; i<=NF; i++)

should be faster this way
Code:
for (i=NF; i; i--)

since usually the zero check is translated to assembly code that is simpler than that of a less than check.

Ok, to be fair, the better readability of the first outweighs by far the infinitesimal advantage in speed of the second.
# 4  
Old 05-25-2009
Quote:
Originally Posted by colemar
[...]
This one tough
Code:
for (i=1; i<=NF; i++)

should be faster this way
Code:
for (i=NF; i; i--)

since usually the zero check is translated to assembly code that is simpler than that of a less than check.[...]
I didn't know that,
thank you for elaborating on how it works.
# 5  
Old 05-25-2009
Cool, I tested the zero check and less than check - zero check seems to real quick compared to the less than check

Thanks for the insight

Code:
awk '{ NF=9999999; for ( i=1; i<=NF; i++ ) { } }' dummy  50.74s user 0.70s system 97% cpu 52.919 total

Code:
awk '{ NF=9999999; for ( i=NF; i; i-- ) { } }' dummy  31.10s user 0.74s system 95% cpu 33.295 total

# 6  
Old 05-26-2009
if its just for timing the iteration from 1 to 999999, then i guess its ok. however, both output are different and may serve different purposes. One counts up and the other counts down. Therefore in such cases, one will look at the whole context , eg if you want to get the 1000th item for example, you might not want to use the decrement method.
# 7  
Old 05-26-2009
yes, its purely for timing purpose - where the result of looping is immaterial of incremeting or decrementing the counter.

As you said, the case for accessing nth element in m possible values where
Code:
m - n

being almost equal to 0, or n very less compared to m/2 or m/4, it doesnt make sense to choose any of the orders here and applying predefined heuristics in direction of incrementing/decrementing will make sense.

Smilie
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