Compact way to write matrices containing indices

Hi, I have an array A and a matrix B.

(Task 1) First, I would like to check which elements of A are members of the first column of B.

(Task 2) Then, I would like to return (i.e. write down) my matrix B with the same order of the elements of A, and leaving a NaN (or zero) for those elements of A that were not found in B. Is there a compact way to accomplish the Task 2 ?

OK, a little bit messy to explain, but with this example it should be easier to understand what I need:

% Input
A = [3
     4
     9
     1
     5];
  
B = [3 5
     6 2
     4 8
     5 7
     9 7];

% Task (1) - Easy
[~,i] = ismember(A,B(:,1))

% Task (2) - First naive attempt gives an error
>> B(i,:)

Index in position 1 is invalid. Array indices must be positive integers or logical values.

% Task (2) - A second naive attempt works, but the 4th row of A is missing
>> B(i(i~=0),:)

ans =

     3     5
     4     8
     9     7
     5     7

% Desired Output - Here the 4th row of A is present with a NaN in the
% second column
>> B(?,?)

ans =

     3     5
     4     8
     9     7
     1     NaN
     5     7 

% Is there a compact way to get my desired output?

% Maybe just writing something like:  B(?,?)

[Sim]

Basically, I would like to avoid this loop:

% Task (1)
[~,i] = ismember(A,B(:,1));
% Task (2) - Desired Output
for j = 1 : length(i)
    if i(j)~=0
    B_des_output(j,:) = B(i(j),:);
    else
    B_des_output(j,:) = [A(j) NaN];
    end
end

% Result
>> B_des_output

     3     5
     4     8
     9     7
     1   NaN
     5     7

Answer 1

[Stephen23]

A = [3;4;9;1;5];
B = [3,5;6,2;4,8;5,7;9,7];
[X,Y] = ismember(A,B(:,1));
M = A;
M(:,2) = NaN;
M(X,2) = B(Y(X),2)

M = 5×2

3 5 4 8 9 7 1 NaN 5 7

[Sim]

All great solutions @David Hill and @Stephen, but this one looks like even more compact than other ones!

Many thanks to everyone for your contribution, I would accept all the answers :)

Answer 2

[David Hill]

[~,idx]=ismember(A,B(:,1));
f=find(idx==0);
idx(idx==0)=1;
C=B(idx,:);
C(f,:)=[A(f),nan(length(f),1)];

[Sim]

@David Hill Coooooolll !!! Many thanks :)