Counting the number of atoms for an element in a chemical formula

have a look at this project

For your simple case, I constructed this and it seems to work, i.e., the function extracts the number behind the species letter:

For example:

You might need to deal with the case of no digit(s) after the element.

I was working on the following when the replies were posted:

Thank you so much, tony, chozo and KurtB for these awesome suggestions! I am going to try them out and let you know in case I'm still stuck. Really appreciate the help! 

I would probably search through the string one character at a time.

1. The first character should be upper case
2. Check if the next character is lower case, numeric or upper case
3. Save lower case, if present
4. Save numeric, if present
5. Once you reach a new upper case character you start from 1

At the end you probably want to check the letter combinations against a list of valid elements

You already got good advise, just to mention that olelytken's strategy is implemented in the function ElementCount(str) below:

https://www.wavemetrics.com/code-snippet/molar-weight-calculator

There are smarter alternatives for the regex parts but it works.

@tony - very neat solution. I never knew SplitString could nibble bits off like that.

One learns something every day!

Thanks all again for your excellent solutions! 

@tony: thanks! Upon running elementlist ("C6H10O5"), I get C:6; H:10;O:5; as a text solution which is great. However, I want to store the counts in specific numeric waves so I could calculate the O:C, N:C, S:C ratios etc. 

One quick issue is that the output from elementlist will have or miss elements depending on which ones are present in the chemical formula. So how to assign element counts to individual numeric waves for each element? 

For example, I have a 1D wave with chemical formulas. Now I want 5 other 1D waves (or lets say 1 2D wave with 5 columns) where each column stores numeric count values of C, H, O, N, S. When an element is not present in the formula, it gets assigned a value of NaN in the 2D wave. I think if I start with a fully NaNed 2D wave, that will take care of the assigning NaNs to absent elements. However, I still need to assign the result from the text output as numeric values in individual columns of the 2D wave. 

Actually I haven't used "Numberbykey" much before so this is quite a learning experience for me. Not sure how to extract numbers from your code and assign them to 1D waves.. 

Kindly advise (all). Thanks a ton! 

If you want to use the keylist approach you can extract values from the list using the NumberByKey function. So you could put the keylists in a textwave and then write something like Wave2D[][%C] = NumberByKey("C", ListWave). But, if you're working with waves, you may be better off with chozo's approach: Wave2D[][%C] = countAtoms(FormulaWave, "C").

If the columns have elements as dimension labels you can also write

Wave2D = countAtoms(FormulaWave[p], GetDimLabel(Wave2D, 1, q))

Edit: I mixed up the names of the functions by chozo and KurtB

If you will choose my code, rather use the revised function below, which can also count single atoms:

And, for completeness, there's this horribly inefficient version:

Wave2D = NumberByKey(GetDimLabel(Wave2D, 1, q), elementlist(FormulaWave[p]))

Thanks a lot, tony and chozo, for your responses. Below is what I have set up based on your codes, which does the job. I am going to read up more on the NumberbyKey function: 

Function elements(specieswave)

wave/t specieswave

variable i,j,num = dimsize(specieswave,0)

dfref dfr=root:Parameters:

svar/sdfr=dfr elements

variable ecount = itemsinlist(elements)

make/d/o/n=(num,ecount)elementscount = nan

make/d/o/n=(num,ecount-1)elementsratios = nan

for(i=0;i<ecount;i+=1)

SetDimLabel 1,i,$stringfromlist(i,elements),elementscount

endfor 

for(i=1;i<ecount;i+=1)

SetDimLabel 1,i-1,$stringfromlist(i,elements)+"/C",elementsratios

endfor 

for(j=0;j<ecount;j+=1)

for(i=0;i<num;i+=1)

elementscount[i][%$stringfromlist(j,elements)] = countAtoms(specieswave[i],stringfromlist(j,elements))

endfor

endfor

for(j=1;j<ecount;j+=1)

elementsratios[][%$stringfromlist(j,elements)+"/C"] = elementscount[p][%$stringfromlist(j,elements)]/elementscount[p][0]

endfor

elementsratios = numtype(elementsratios) == 1 ? nan : elementsratios

edit elementsratios

edit elementscount

end 

Note that you can use an implicit loop rather than nested loops to set values in a wave:

Thanks, tony! I'd certainly prefer to cut out multiple loops wherever possible. This helps a lot. 

Tony-

That is amazingly elegant!! Been trying to develop similar code, but without using GrepString.

Thanks,

-Steve