How to search and find nearest data in the given array

I have an array (Matt J attached)

I have n = 70; or any other number. SP = 998.45 or any other number from column2. I want to search and find corresponding row in column2 contains 998.45 or other number with nearest value of column1 in finded rows with n =70 or any other number. Please help me.

           70          987       984.65          0.1       139.72
           43       987.05        984.6         0.19        89.81
           70       987.05        984.7          0.1       139.72
           70       987.05        984.7          0.1       139.72
           43        987.1       984.65         0.18         89.8
           70        987.1       984.75          0.1       139.72
           43       987.15        984.7         0.18         89.8
           70       987.15        984.8          0.1       139.72
           43        987.2       984.75         0.18         89.8
           70        987.2       984.85          0.1       139.72
           43       987.25        984.8         0.18         89.8
           70       987.25        984.9          0.1       139.72
           43        987.3       984.85         0.18         89.8
...

[dpb]

Sorry, the explanation is too disjointed to undersaand.

What would your result be expected to be for the above inputs and, how, precisely would that have been determined to be the correct answer?

[Triveni]

There are three rows containing 998.45 in column no. 2.

In these three rows, I want to find nearest value of 70.

Answer 1

[Voss]

load('array.mat')

n = 70;
SP = 998.45;

% find the rows where column 2 of array is SP
matching_rows = find(array(:,2) == SP)

matching_rows = 3×1

541 542 543

% find the index of the value nearest to n
% in column 1, among those rows of array
[~,idx] = min(abs(array(matching_rows,1) - n))

idx = 2

% get the value
result = array(matching_rows(idx),1)

result = 62