How to count the number of times that the previous observation was repeated

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Mia Dier 2021-1-9

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https://ww2.mathworks.cn/matlabcentral/answers/712638-how-to-count-the-number-of-times-that-the-previous-observation-was-repeated

评论： Rik 2021-1-15

采纳的回答： Cris LaPierre

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I have a table that looks like this:

country_id year M

1 2000 10

1 2001 10

1 2002 NaN

1 2003 15

1 2004 10

1 2005 10

2 2002 5

2 2003 5

2 2004 20

2 2005 10

2 2006 5

And I want to calculate the number of years that the previous year's M value was repeated in the last 5 years. That is,

country_id year M prev_count

1 2000 10 NaN

1 2001 10 1

1 2002 NaN 2

1 2003 15 NaN

1 2004 10 1

1 2005 10 2

2 2002 5 NaN

2 2003 5 1

2 2004 20 2

2 2005 20 1

2 2006 5 2

I can't run the code below because the count function works only for strings. Is there a function that can be used alternatively?

prev_count=NaN(N,1);
for i=1:5
    for k=i+1:N
        if myTable{k,'country_id'} == myTable{k-i,'country_id'} 
            prev_count(k,1)=count(M(k-i:k-1,1), country_id(i,1));  
        end
    end
end

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Rik 2021-1-15

The mere fact that you have a follow-up question doesn't make this one a duplicate.

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采纳的回答

Cris LaPierre 2021-1-9

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/712638-how-to-count-the-number-of-times-that-the-previous-observation-was-repeated#answer_594253

编辑：Cris LaPierre 2021-1-9

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Use logical indexing and sum the true cases.

for r = 1:height(myTable)
    T = myTable.country_id == myTable.country_id(r) & ...
        myTable.year >= myTable.year(r)-5 & ...
        myTable.year < myTable.year(r) & ...
        myTable.M == myTable.M(r);
    myTable.prev_count(r) = sum(T);
end

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Cris LaPierre 2021-1-9

编辑：Cris LaPierre 2021-1-9

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Ok, so just update the code I shared to meet your criteria.

for r = 2:height(myTable)
    T = myTable.country_id == myTable.country_id(r) & ...
        myTable.year >= myTable.year(r)-4 & ...
        myTable.year < myTable.year(r) & ...
        myTable.M == myTable.M(r-1);
    myTable.prev_count(r) = sum(T);
end
myTable.prev_count(myTable.prev_count==0) = NaN