"Evenly dividing array elements in bash": comment by Vidar Bashman Madsen

Thu, 29 Mar 2007 06:54:26 PDT

Lacking a preview option and no info on tags, I hope this is formatted properly... How about this approach; Iterate through the items, if item_number % days = today, process item. The code:


 i=0
 for item in ${items[@]}; do
   if [ $[$i % $days] = $today ]; then
     echo "Process $item..."
   fi
   i=$[$i+1]
 done

"Evenly dividing array elements in bash" by triley

Tue, 27 Mar 2007 13:08:00 PDT

Writing in bash is fun because of the constraints it offers, but I’m never sure if I am choosing the most straightforward way to do things.

A few weeks ago I had to write a script to vacuum a bunch of databases once per week. Instead of doing them all at once, I wanted to evenly spread the load across the seven days.

I wrote something that works pretty well, I think, but it does seem a little hackish, and I’d love to hear if there is a better way to achieve this.

Here’s what I did, check it out:

 # 11 elements in this example
 # Should be processed 2 per day for the first 4 days, then 1 per day for the reamining 3 days
 items=("mario" "luigi" "toad" "peach" "yoshi" "wario" "koopa" "bowser" "lakitu" "birdo" "fryguy")

 days=7

 # number of the current day, starting from 0
 let "today = `date +%u` - 1" 

 # number of whole that can be processed per day
 let "per_day = ${#items[*]} / ${days}" 

 # remainder of items that must also be processed
 let "remainder = ${#items[*]} % ${days}" 

 # index of array element to start iterating from for the current day
 if [ $today -gt $remainder ]; then
   let "start = (${per_day} * ${today}) + ${remainder}" 
 else
   let "start = (${per_day} * ${today}) + ${today}" 
 fi

 # number of elements to iterate over for the current day
 if [ $today -ge $remainder ]; then
   count=$per_day
 else
   let "count = ${per_day} + 1" 
 fi

 # Do it!
 echo "Processing ${count} items." 

 for ((i=$start; i < ($start+$count); i++)); do
   do_something_with_item ${items[$i]}
 done

If you can offer any tips or suggestions, please comment on this entry!

Blah Blah Woof Woof comments on Evenly dividing array elements in bash

"Evenly dividing array elements in bash": comment by Vidar Bashman Madsen

"Evenly dividing array elements in bash" by triley