Script is taking 11 - 20 seconds to lookup up an item in an 18,000 row data set - hash

Question

I have two Google sheets workbooks.
One is the "master" source of lookup data with a key based on manufacturer item #, which could be anything from 1234 to A-01/234-Name_1. This sheet, referenced via SpreadsheetApp.openByUrl, has 18,000 rows and 13 columns. The key column has been converted to plain text and the sheet is sorted by this column.
The second is the "template" where people enter item #s that they need to look up against the master, typically 20 - 1500 items at a time.
The script is in the template. It is very slow and routinely times out after 30 minutes. It was written by someone else and I am new to App Script, but I think I've managed to understand what the script is doing and where the bottleneck is occurring.
It does a bunch of stuff, but this is the meat of the lookup:
var numrows = master.getDataRange().getNumRows();
var masterdata = master.getDataRange().getValues();
var itemnumberlist = template.getDataRange().getValues();
var retreiveddata = [];
// iterate through the manf item number list to find all matches in the
// master and return those matches to another sheet
for (i = 1; i < template.getDataRange().getValues().length; i++) {
for (j = 0; j < numrows; j++) {
if (masterdata[j][1].toString() === itemnumberlist[i][1].toString()) {
retreiveddata.push(data[j]);
anothersheet.appendRow(data[j]);
}
}
}
I used Logger.log() to determine that each time through the i loop is taking 11 - 19 seconds, which just seems insane.
I've been doing some google searching and I've tried a couple of different things...
First I tried moving the writing of found data out of the for loop so the script would be doing all of its reading first and then writing in one big chunk, but I couldn't get it exactly right. My two attempts are below.
var mycounter = 0;
for (i = 0; i < template.getDataRange().getValues().length; i++) {
for (j = 0; j < numrows; j++) {
if (masterdata[j][0].toString() === itemnumberlist[i][0].toString()) {
retreiveddata.push(masterdata[j]);
mycounter = mycounter + 1;
}
}
}
// Attempt 1
// var myrange = retreiveddata.length;
// for(k = 0; k < myrange; k++) {
// anothersheet.appendRow(retreiveddata.pop([k]);
// }
//Attempt 2
var myotherrange = anothersheet.getRange(2,1,myothercounter, 13)
myotherrange.setValues(retreiveddata);
I can't remember for sure, because this was on Friday, but I think both attempts resulted in the script trying to write the entire master file into "anothersheet".
So I temporarily set this aside and decided to try something else. I was trying to recreate the issue in a couple of sample spreadsheets, but I was unable to do so. The same script is getting through my 15,000 row sample "master" file in less than 1 second per lookup. The only thing I can think of is that I used a random number as my key instead of a weird text string.
That led me to think that maybe I could use a hash algorithm on both the master data and the values to be looked up, but this is presenting a whole other set of issues.
I borrowed these functions from another forum post:
function GetMD5Hash(value) {
var rawHash = Utilities.computeDigest(Utilities.DigestAlgorithm.MD5,
value);
var txtHash = '';
for (j = 0; j <rawHash.length; j++) {
var hashVal = rawHash[j];
if (hashVal < 0)
hashVal += 256;
if (hashVal.toString(16).length == 1)
txtHash += "0";
txtHash += hashVal.toString(16);
Utilities.sleep(100);
}
return txtHash;
}
function RangeGetMD5Hash(input) {
if (input.map) { // Test whether input is an array.
return input.map(GetMD5Hash); // Recurse over array if so.
Utilities.sleep(100);
} else {
return GetMD5Hash(input)
}
}
It literally took me all day to get the hash value for all 18,000 item #s in my master spreadsheet. Neither GetMD5Hash nor RangeGetMD5Hash will return a value consistently. I can only do a few rows at a time. Sometimes I get "Loading..." indefinitely. Sometimes I get "#Name" with a message about GetMD5Hash being undefined (despite the fact that it worked on the previous row). And sometimes I get "#Error" with a message about an internal error.
This method actually reduces the lookup time of each item to 2 - 3 seconds (much better, but not great). However, I can't get the hash function to consistently work on the input data.
At this point I'm so frustrated and behind on my other work that I thought I'd reach out to the smart people on these forums and hope for some sort of miracle response.
To summarize, I'm looking for suggestions on these three items:
What am I doing wrong in my attempt to move the write out of the for loop?
Is there a way to get my hash value faster or utilize a different method to accomplish the same goal?
What else can I try to help speed up the script?
Any suggestions you can offer would be greatly appreciated!
-Mandy

Answer 1

It sounds like you hit on the right approach with attempting to move the appendRow() call out of the loop. Anytime you are reading or writing to a spreadsheet you can expect the individual call to take 1 to 2 seconds, so this will eat up a lot of time when you get matches. Storing the matches in an array and writing them all at once is the way to go.
Another thing I notice is that your script calls getValues() in the actual for loop condition statement. The condition statement is executed each time on each iteration of the loop, so this is potentially wasting a lot of time even when you don't have matches.
A final tweak that may be helpful depending on your desired behaviour. You can stop the inner for loop after it finds the first match, which, if you only care about the first match or know there will only be one match, will save you a lot of iterations. To do this, put "break" immediately after the retreiveddata.push(masterdata[j]); line.
To fix the getValues issue, Change:
for (i = 1; i < template.getDataRange().getValues().length; i++) {
To:
for (i = 1; i < itemnumberlist.length; i++) {
And that fix along with the appendRow issue, and including the break call:
for (i = 1; i < itemnumberlist.length; i++) {
for (j = 0; j < numrows; j++) {
if (masterdata[j][0].toString() === itemnumberlist[i][0].toString()) {
retreiveddata.push(masterdata[j]);
break; //stop searching after first match, move on to next item
}
}
}
//make sure you have data to write before trying to write it.
if(retreiveddata.length > 0){
var myotherrange = anothersheet.getRange(2,1,retreiveddata.length, retreiveddata[0].length);
myotherrange.setValues(retreiveddata);
}
If you are re-using the same sheet for "anothersheet" on each execution, you may also want to call anothersheet.clear() to erase any existing data before you write your fresh results.
I would pass on the hashing approach altogether, comparing strings is comparing strings, so whether they are hashes or actual part numbers I wouldn't expect a significant difference.