Simple Way to Find How Far Down a Number Is

Hello,

I was wondering if there is a simple way to determine which row a number appears?

For example, if I have a large table with the last column is either a 1 or 0, if I want to know which row holds a 0, how can I make an array that essentially says: The value 0 appears in rows 1, 34, 89, ...

I found this forum post, which goes over how to pull a number from a column of the same row based on the value in another column.

I was thinking I could make a new column that just numbers from 1 to N (where N is the number of rows) and add that as a new column to the table.

Then using the technique from the linked forum post, save the number (value) from the added column into an empty matrix (an all-zero array from 1 to N).

Then after that, remove all the zeros and be left with an array that only has the postitions of where the 0 is in the original column.

This method seems long but it can work, I was just wondering if there is something simpler to do.

Thanks.

Answer 1

[Star Strider]

Use the find function —

T1 = array2table([rand(10,3) randi([0 1], 10, 1)])

T1 = 10×4 table
     Var1       Var2       Var3      Var4
    _______    _______    _______    ____

    0.63964    0.82422    0.12981     0  
      0.591    0.70306    0.62215     0  
    0.51874    0.22951    0.43027     0  
    0.42188    0.80246    0.65887     1  
    0.14287    0.80063     0.2118     0  
    0.73422    0.92003    0.11586     1  
    0.67137    0.43841    0.50498     1  
    0.52176    0.91758     0.3801     0  
    0.12744    0.61668    0.65305     0  
    0.45125    0.19285    0.96927     0  

RowIdx = find(T1.Var4 == 0)

RowIdx = 7×1

1 2 3 5 8 9 10

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[Jon]

Sweet, thank you very much.

That is much simpler than what I though about doing.

[Star Strider]

As always, my pleasure!