Change the first half of consecutive 1 in a column into 2

I have a matrix with 31 rows and around 500 columns. The matrix has NaN, 0s and 1s. The 1s are always consecutive in each column, but the number is not always the same. There are also some columns without 1s.

I need to find the 1s in each column, count them and calculate the half, then I ned to change the first half into 2s, but the second half of 1s should stay as 1s.

Answer 1

[Matt J]

map=(A==1);

C=cumsum(map,1,'omitnan');

A( C<=C(end,:)/2 & map) = 2;

[Ana Maria Alzate]

Thank you! The lines work perfect.

Just one question, right now, if the column have an odd number of 1s, it changes less than the half to 1 and it would be better if it is the opposite. For example, if there are 9 number 1, it is better 5 2s and 4 1s, but now I am getting 4 1s and 5 2s.

[Matt J]

Just use ceil().