Method to count number of observations by category

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Kate
Kate 2014-6-26
评论： Kate 2014-6-27
What would be the best method to count observations which fit the criteria number listed in the last column:
>> s
s =
22.9924 46.8888 1.4597 4.8547 1.3379 3.8795 24.8686 3.0000
19.7965 40.1072 1.4644 5.2458 1.3262 3.0253 19.7573 3.0000
12.0315 70.3394 1.8392 3.6708 1.2664 2.2959 13.2066 3.0000
0.0854 4.4000 1.3399 1.6076 1.2214 1.9499 1.7144 2.0000
-10.7796 26.7116 1.0871 1.0044 1.2722 1.6683 -12.4818 1.0000
1.3617 15.7695 1.0896 1.4550 1.2444 1.9098 1.2284 2.0000
14.2101 11.4473 1.2464 4.0444 1.2413 2.6900 16.6996 3.0000
12.9187 60.9303 1.5128 3.4454 1.2593 2.2976 15.4214 3.0000
4.8807 11.4097 1.4971 2.0412 1.2105 1.7832 5.7704 2.0000
5.7536 22.7122 1.1432 1.8351 1.2305 2.1097 9.1543 3.0000
another example:
s =
-3.8660 3.8000 1.8212 1.0659 0.9359 1.1195 -4.2488 4.0000
5.6911 1.6000 1.8920 1.0000 1.0772 1.1631 7.5085 6.0000
1.6582 31.9250 1.1889 1.0221 1.1091 1.1899 2.0074 5.0000
-3.0589 1.1000 1.6842 1.0184 0.9804 1.1165 -4.5364 4.0000
Such that I will have an alert that I only have one observation of , say 1.00 in the first piece of data, but 5 and 6 in the second piece?
Thanks, Kate

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采纳的回答

Cedric
Cedric 2014-6-27
编辑：Cedric 2014-6-27
How about
counts = accumarray( s(:,end), 1 ) ;
In the first case, it gives
counts =
1
3
6
In the second case
counts =
0
0
0
2
1
1
As you can see, the i-th element of vector counts is the count of data i. And then you can process counts as you want/need, e.g.
is1 = counts == 1 ;
if any( is1 )
fprintf( 'Warning, the following data blabla..\n' ) ;
disp( find( is1 )) ;
end

更多回答（2 个）

Image Analyst
Image Analyst 2014-6-26
编辑：Image Analyst 2014-6-26
I believe this is what you want:
s =[...
22.9924 46.8888 1.4597 4.8547 1.3379 3.8795 24.8686 3.0000
19.7965 40.1072 1.4644 5.2458 1.3262 3.0253 19.7573 3.0000
12.0315 70.3394 1.8392 3.6708 1.2664 2.2959 13.2066 3.0000
0.0854 4.4000 1.3399 1.6076 1.2214 1.9499 1.7144 2.0000
-10.7796 26.7116 1.0871 1.0044 1.2722 1.6683 -12.4818 1.0000
1.3617 15.7695 1.0896 1.4550 1.2444 1.9098 1.2284 2.0000
14.2101 11.4473 1.2464 4.0444 1.2413 2.6900 16.6996 3.0000
12.9187 60.9303 1.5128 3.4454 1.2593 2.2976 15.4214 18.0000
4.8807 11.4097 1.4971 2.0412 1.2105 1.7832 5.7704 2.0000
5.7536 22.7122 1.1432 1.8351 1.2305 2.1097 9.1543 3.0000]
category = s(:, end); % Extract last column
% Get histogram of it.
edges = unique(category); % Edges of histogram
counts = histc(category, unique(category))
% Find indexes for which the count is 1.
singleCounts = find(counts == 1)
for k = 1 : length(singleCounts)
thisIndex = singleCounts(k);
numberAtIndex = edges(thisIndex);
message = sprintf('The category %d shows up only once!', numberAtIndex);
uiwait(helpdlg(message));
end
It takes the histogram of the last column. Any number that shows up in that column only one time will popup a message to the user. I changed your s slightly so that the number 1 and the number 18 each show up only once in the last column.
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Image Analyst
Image Analyst 2014-6-27
编辑：Image Analyst 2014-6-27
Kate, my code runs fine on your new, additional example with 5 and 6. Here, look at this:
s =[...
-3.8660 3.8000 1.8212 1.0659 0.9359 1.1195 -4.2488 4.0000
5.6911 1.6000 1.8920 1.0000 1.0772 1.1631 7.5085 6.0000
1.6582 31.9250 1.1889 1.0221 1.1091 1.1899 2.0074 5.0000
-3.0589 1.1000 1.6842 1.0184 0.9804 1.1165 -4.5364 4.0000]
category = s(:, end); % Extract last column
% Get histogram of it.
edges = unique(category); % Edges of histogram
counts = histc(category, edges )
% Find indexes for which the count is 1
singleCounts = find(counts == 1)
for k = 1 : length(singleCounts)
thisIndex = singleCounts(k);
numberAtIndex = edges(thisIndex);
message = sprintf('The category %d shows up only once!', numberAtIndex);
fprintf('%s\n', message);
uiwait(helpdlg(message));
end
In addition to the popup message box, you'll see this in the command window:
s =
-3.8660 3.8000 1.8212 1.0659 0.9359 1.1195 -4.2488 4.0000
5.6911 1.6000 1.8920 1.0000 1.0772 1.1631 7.5085 6.0000
1.6582 31.9250 1.1889 1.0221 1.1091 1.1899 2.0074 5.0000
-3.0589 1.1000 1.6842 1.0184 0.9804 1.1165 -4.5364 4.0000
counts =
2
1
1
singleCounts =
2
3
The category 5 shows up only once!
The category 6 shows up only once!
Tell me if this doesn't do exactly and perfectly what you want to do and you asked for.
Kate
Kate 2014-6-27
Thanks Image Analyst, the new code works. I had run it on your previous code when I replied.

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Ben11
Ben11 2014-6-26
what about:
size(s(s == 1.00),1))
which would give you the number of occurences in s meeting the criterion.
Or maybe something like this
if any(s(s == 1.00))
msgbox('we have a winner')
end
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Ben11
Ben11 2014-6-26
Ok I'm not quite sure to understand sorry. If we take your matrix above for example, would you like to know how many times the value in the last column is present in the corresponding row? Or in the whole matrix? Or would you like to know that there are six 3's, three 2's and one 1?
Kate
Kate 2014-6-26
To illustrate my question, here is a different piece of data. Here I would want to know that 5 and 6 are only seen once:
s =
-3.8660 3.8000 1.8212 1.0659 0.9359 1.1195 -4.2488 4.0000
5.6911 1.6000 1.8920 1.0000 1.0772 1.1631 7.5085 6.0000
1.6582 31.9250 1.1889 1.0221 1.1091 1.1899 2.0074 5.0000
-3.0589 1.1000 1.6842 1.0184 0.9804 1.1165 -4.5364 4.0000

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