CODEWITHSUNDEEP
iphoneobjective-c
Ian Oswald
Ian Oswald

Reputation: 1375

Convert string fraction to decimal

I have a plist file that I am reading out a measurement, but some of the measurements are fractions such as 6 3/8". I formatted them that way because it's easier to find that on a tape measure than it is to find 6.375". My problem is now I want to do a conversion to metric on the fly and it isn't reading in the fraction part of the number. My current code is this.

cutoutLabel.text = [NSString stringWithFormat:@"%.2f mm. %@", [[[sizeDict valueForKey:Sub_Size] objectForKey:@"Cutout Dimensions"]floatValue] * 25.4, [temp objectAtIndex:2]];

Thanks.

Upvotes: 2

Views: 1199

Answers (3)

JeffB6688
JeffB6688

Reputation: 3880

Building on Ian's answer and trying to be a little more complete (since his example was for a whole number and fractional part with an inch character (6 3/8"), I suggest the following method (it also works if there are spaces before the whole number:

// Convert a string consisting of a whole and fractional value into a decimal number
-(float) getFloatValueFromString: (NSString *) stringValue {

// The input string value has a format similar to 2 1/4". Need to remove the inch (") character and
// everything after it.
NSRange found = [stringValue rangeOfString: @"\""];    // look for the occurrence of the " character
if (found.location != NSNotFound) {
    // There is a " character. Get the substring up to the "\"" character
    stringValue = [stringValue substringToIndex: found.location];
}

// Now the input format looks something like 2 1/4. Need to convert this to a float value
NSArray *temp = [stringValue componentsSeparatedByString:@" "];
float convertedFraction = 0;
float wholeNumber = 0;
for (int i=0; i<[temp count]; i++) {
    if ([[temp objectAtIndex:i] isEqualToString:@""]) {
        continue;
    }
    NSArray *fraction = [[temp objectAtIndex:i]componentsSeparatedByString:@"/"];
    if ([fraction count] > 1) {
        convertedFraction = [[fraction objectAtIndex:0]floatValue]/[[fraction objectAtIndex:1]floatValue];
    }
    else if ([fraction count] == 1) {
        wholeNumber = [[fraction objectAtIndex:0] floatValue];
    }
}

convertedFraction += wholeNumber;

return convertedFraction;
}

Upvotes: 0

Ian Oswald
Ian Oswald

Reputation: 1375

That's what I ended up doing.

NSArray *temp = [[[sizeDict valueForKey:Sub_Size] objectForKey:@"Cutout Dimensions"] componentsSeparatedByString:@" "];
        if ([temp count] > 2) {
            NSArray *fraction = [[temp objectAtIndex:1]componentsSeparatedByString:@"/"];
            convertedFraction = [[fraction objectAtIndex:0]floatValue]/[[fraction objectAtIndex:1]floatValue];
        }

Upvotes: 4

Jesse Black
Jesse Black

Reputation: 7976

You can get the numerator and denominator as follows:

NSRange slashPos = [fraction.text rangeOfString:@"/"];

NSString * numerator = [fraction.text substringToIndex:slashPos.location];
NSString * denominator = [fraction.text substringFromIndex:slashPos.location+1];

You should take more care than this, check that your range is of length 1 and make sure that the string has characters after the "/" character. But if you know you are feeding this code a fraction string it should work in your case

The idea is in place, but you will also need to apply the same logic first to separate the whole number from you fraction. Apply the same logic, searching for a @" " and then find the numerator and denominator

Upvotes: 1

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