Execute an arithmetic expression in Android

Question

I want to do an arithmetic operation on data stored in an Array.
User may choose random column and random operation on them.
like,

String DataTmp[10][3] = ...;
String strCalc = "Float.parseFloat(DataTmp[i][0]) + Float.parseFloat(DataTmp[i][2]) * Float.parseFloat(DataTmp[i][1])";

Is there any way to achieve this?

Edited: The calculation mentioned above is for example. It is not the fixed calculation. It may change anyway like,

String strCalc = "Float.parseFloat(DataTmp[i][1]) / Float.parseFloat(DataTmp[i][2])";

or

String strCalc = "(Float.parseFloat(DataTmp[i][2]) - Float.parseFloat(DataTmp[i][1])) / Float.parseFloat(DataTmp[i][1])";

So i can't just do that dynamic calculate. I need to execute the expression inside the String.

Further Edited:

User have a textbox to enter the calculation.
So, the user will enter something like "(field 1 - field 3)/field 2" or anything as they wish.
I need to take the corresponding value for fields from array and apply the operation (+,-,*,/) as per the user's selection.
Everything in this expression is dynamic, including the field order and operations.

Solution Implemented: here is the long possible solution i reached. add improvements if you've any. i didn't implement the hierarchy of calculation based on parenthesis.

              strCalc = strCalc.replace("(", "");
              strCalc = strCalc.replace(")", "");

              List<String> calcList = new ArrayList<String>(Arrays.asList(strCalc
                          .split(" ")));
              showInfo("List Size : " + calcList.size());
              // Doing multiplication and division first
              for (int i = 0; i < calcList.size(); i++) {
                    String curStr = calcList.get(i);
                    if (curStr.compareTo("*") == 0) {
                          float val1 = Float.parseFloat(calcList.get(i - 1));
                          float val2 = Float.parseFloat(calcList.get(i + 1));
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          float result = val1 * val2;
                          calcList.add(i - 1, "" + result);
                          i--;
                          continue;
                    }
                    if (curStr.compareTo("/") == 0) {
                          float val1 = Float.parseFloat(calcList.get(i - 1));
                          float val2 = Float.parseFloat(calcList.get(i + 1));
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          float result = val1 / val2;
                          calcList.add(i - 1, "" + result);
                          i--;
                          continue;
                    }
              }
              // Doing addition and subtraction next
              for (int i = 0; i < calcList.size(); i++) {
                    String curStr = calcList.get(i);
                    if (curStr.compareTo("+") == 0) {
                          float val1 = Float.parseFloat(calcList.get(i - 1));
                          float val2 = Float.parseFloat(calcList.get(i + 1));
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          float result = val1 + val2;
                          calcList.add(i - 1, "" + result);
                          i--;
                          continue;
                    }
                    if (curStr.compareTo("-") == 0) {
                          float val1 = Float.parseFloat(calcList.get(i - 1));
                          float val2 = Float.parseFloat(calcList.get(i + 1));
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          calcList.remove(i - 1);
                          float result = val1 - val2;
                          calcList.add(i - 1, "" + result);
                          i--;
                          continue;
                    }
              }
              return calcList.get(0);

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score 0 · Answer 1 · answered Nov 16 '11 at 16:44

0

The way you chose should work

float result = Float.parseFloat(DataTmp[i][0]) + Float.parseFloat(DataTmp[i][2]) * Float.parseFloat(DataTmp[i][1]);
String strCalc = String.valueOf(result);

But you need to be careful: make sure you actually have floats in your DataTmp array (by checking them before doing the operation), and you may also want add some formatting to the result.

answered Nov 16 '11 at 16:44

Guillaume

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the calculation part i mentioned is not a fixed one. i've updated my problem. thanks for replying. – BobbyGoks Nov 16 '11 at 16:58
Your update doesn't really address the problem: do you mean that the operations to do are themselves dynamic? Are you trying to code a calculator or something like that? If so you'd need a reference to the operations you want to do (possibly in an enum), and do the relevant operations according to the user's choice. Please explain in a bit more details what you are exactly trying to achieve – Guillaume Nov 16 '11 at 17:23
"the operations to do are themselves dynamic" - this is what i'm trying to achieve. user have a textbox to enter the calculation. so, the user will enter something like "(field 1 - field 3)/field 2" or anything as they wish. i need to take the corresponding value for fields from array and apply the operation (+,-,*,/) as per the user's selection. – BobbyGoks Nov 16 '11 at 17:32
OK, so you need to parse the user input, extract operations and operands, and apply that - it's a lot more complex, I would suggest test-driving it and adding support for different operations iteratively. I may want to think of something and post a new answer. – Guillaume Nov 16 '11 at 21:06
ok Guillaume. i thought iterative way will be complex, thats why i asked the question. now, with no other option, i'm going to implement that. let me know if you come up with any solution. Thanks for you attempts. – BobbyGoks Nov 17 '11 at 09:23

score 0 · Answer 2 · answered Nov 16 '11 at 16:45

0

Index the random column and row in the DataTmp array and then just do the calculation. Make sure you are casting correctly since you are using string arrays.

answered Nov 16 '11 at 16:45

prolink007

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"then just do the calculation" - prolink007 doing the calculation is the problem. seems my problem is unclear. i've corrected it now. thanks for replying. – BobbyGoks Nov 16 '11 at 16:56
"I need to execute the expression inside the String." - why? You could do what Guillaume suggested and do the calculation and then convert it to string and set it then. What is wrong with that? – prolink007 Nov 16 '11 at 17:02

Execute an arithmetic expression in Android

2 Answers2