Need help filtering csv by values inside column

I have a large csv file(1034361x28). I want to look at column #1, and find rows containing the same column1 value and find the minimum value of column 2 for the new data set.

simple Ex.

if i have:

2 23

2 39

2 40

5 12

5 9

9 29

9 85

I need the code to find the minimum values for each subset of column 2(min of (23,39,40) and (12,9) and (29,85)).

How would i do so for a 1034361x28 file?

Thank You

Answer 1

[Star Strider]

Try this:

A = [2    23
     2    39
     2    40
     5    12
     5    9
     9    29
     9    85];

[UA1,~,Ix] = unique(A(:,1));
Col2Max = accumarray(Ix, A(:,2), [], @min);
Out = [UA1, Col2Max];

producing:

Out =
     2    23
     5     9
     9    29

[Conor Nelson]

Worked like a charm. Thank You

[Star Strider]

As always, my pleasure!

[Conor Nelson]

Going off this, how can i look through the columns and create a separate array containing the rows with the same col1 values? Would i still use accumarray but without the @min?

[Star Strider]

‘Would i still use accumarray but without the @min?’

Yes. Only the function changes:

SameCol1 = accumarray(Ix, A(:,2), [], @(x){x});
SameCol1{1}

producing:

ans =
    23
    39
    40

and similarly for the others.

It now creates a cell array of values correspoinding to each value of column 1.

[Conor Nelson]

Sorry i think i worded my question wrong, I am looking to output the entire row containing the values. Ex:

ans =

2 23

2 39

2 40

[Star Strider]

Try this:

SameCol1 = accumarray(Ix, (1:size(A,1)), [], @(x){A(x,:)});
SameCol1{1}

producing:

ans =
     2    23
     2    39
     2    40

And so for the others.