Where to get difficulty data for all crypto coins? I need to get difficulty data and exchange rate for past 10 days for making a graph out of it (i.e., for all coins). Can anyone suggest where can I get it?
I suggest you take a look at CoinWarz's API, you can collect your own set of data for a period of time out of it (say 10 latest days, format it your own way and save it on a spreadsheet). You'll need to generate an API key on their site, and then you could either use your own scripts, or visit the API endpoint manually to collect the data, if you so desire (remember that you need your own API KEY to get the data).

Once you have the data you could generate your own graph within a spreadsheet or your  software of preference.

Recomendations: OpenOffice (info on graphs, download page), LibreOffice (info on making graphs, download page).

Here's the reference for that specific API call (quoted from coinWarz's documentation)


  Mining Profitability API
  
  The Mining Profitability API provides profitability data listed on CoinWarz.com. This >data can be for all coins or for specific hashing algorithms: SHA-256, Scrypt, Scrypt-N, >X11, X13, Keccak, Quark, Groestl, JHA, Blake-256, NeoScrypt, Lyra2RE
  
  API Endpoint
  
  http://www.coinwarz.com/v1/api/profitability/?apikey=YOUR_API_KEY&amp;algo=all
  
  API Call Usage
  This value will be deducted from your API usage limit each time you successfully call this API.
  
  Required Input Parameters
  All input parameters are required and not case sensitive.
  
  Parameter - Data Type - Description
  
  ApiKey - String - Provide your approved API key for this parameter.
  
  Algo - String    - Provide one of the the following values for this parameter: 
  all, sha-256, scrypt, scrypt-n, x11, x13, keccak, quark, groestl, jha, blake-256, >neoscrypt, lyra2re


Remember that each time you either visit the API Endpoint or call it to fetch the info with a script, it'll count as 1 call out of your limit, as noted on their documentation. 

Now the easiest way for you to collect the data if you're not into programming your own stuff, would be to use some REST client extension for your browser such as Postman REST client (If you use a different browser look into their respective stores)

It's fairly easy to get used to and you do not need to code your own scripts. 

Here's an example of how the info would be rendered for to you:



(remember you need to place your own API key in lieu of the placeholder "YOUR_API_KEY")

I recommend you use the JSON and PRETTY options so the data is more human readable.

You can then export this to a CSV file using this awesome tool (JSON to CSV)

This site allows you to pase the JSON data and transfer each value pair to a CSV file

Here an example of how it looks: 



Now you have a (set of, since you need multiple days) CSV file that you can use for graph creation using the aforementioned Office Suite Tools.

Hope you'll find this helpful, and good luck!