How to extract row intervals from a table to create a new one.

if I have a table

T:
v1    v2    v3    v4
a     1     1     5
b     3     3     7
c     2     5     7
d     5     5     2
e     5     7     7

How could i obtain all the columns from b and d rows as T2 table?

   T2:
  v1    v2    v3    v4
  b     3     3     7
  c     2     5     7
  d     5     5     2

Answer 1

[Walter Roberson]

T2 = T1(2:4,:);

[Philippe Corner]

Thanks man, but the idea is to Match the first column with b and d

[Walter Roberson]

first_row = find(T1.v1 == b, 1, 'first');
last_row = find(T1.v1 == d, 1, 'first');
if isempty(first_row); error('b not found'); end
if isempty(last_row); error('d not found'); end
if first_row > last_row
  row_vec = first_row : -1 : last_row;
else
  row_vec = first_row : last_row;
end
T2 = T1(row_vec, :);

I had to make arbitrary decisions about what you wanted done if one of the values was missing, or if the values appear in the other order.

[Philippe Corner]

Thanks Mr. Walter, it is showing a mistake due to the == when I adapted it to my code.. do you have an idea why could it be?

[Walter Roberson]

The == could have difficulty depending on the data type involved. Perhaps you need

first_row = find(strcmp(T1.v1, 'b'), 1, 'first');
last_row = find( strcmp(T1.v1, 'd'), 1, 'first');

Answer 2

[Peter Perkins]

Walter interpreted "all the columns from b and d rows" as "FROM b TO d". I'm going to interpret it as "b AND d".

If the first variable in T has unique values, turn it into the row names, and just subscript:

T.Properties.RowNames = T.Var1;
T.Var1 = [];
t({'b' 'd'},:)

If they're not unique, use ismember to create a logical vector to use as a row subscript.

[Walter Roberson]

No, notice they wanted three lines of results, which can only be explained by wanting a range.

[Peter Perkins]

right you are.