Hadoop not all values get assembled for one key - hadoop

Question

I have some data that I would like to aggregate by key using Mapper code and then perform something on all values that belong to a key using Reducer code. For example if I have:
key = 1, val = 1,
key = 1, val = 2,
key = 1, val = 3
I would like to get key=1, val=[1,2,3] in my Reducer.
The thing is, I get something like
key = 1, val=[1,2]
key = 1, val=[3]
Why is that so?
I thought that all the values for one specific key will be assembled in one reducer, but now it seems that there can be more key, val [ ] pairs, since there can be multiple reducers, is that so?
Should I set number of reducers to be 1?
I'm new to Hadoop so this confuses me.
Here's the code
public class SomeJob {
public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException
{
Job job = new Job();
job.setJarByClass(SomeJob.class);
FileInputFormat.addInputPath(job, new Path("/home/pera/data/input/some.csv"));
FileOutputFormat.setOutputPath(job, new Path("/home/pera/data/output"));
job.setMapperClass(SomeMapper.class);
job.setReducerClass(SomeReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(Text.class);
job.waitForCompletion(true);
}
}
public class SomeMapper extends Mapper<LongWritable, Text, Text, Text>{
#Override
protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
String line = value.toString();
String parts[] = line.split(";");
context.write(new Text(parts[0]), new Text(parts[4]));
}
}
public class SomeReducer extends Reducer<Text, Text, Text, Text>{
#Override
protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
String properties = "";
for(Text value : values)
{
properties += value + " ";
}
context.write(key, new Text(properties));
}
}