# Extracting data from an array

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Matt Tomei am 22 Okt. 2020
Beantwortet: Sindar am 23 Okt. 2020
I am interested in plotting a curve to show the path of a point (B) on a rotating gear. This gear is attahced to an arm that makes one full revolution.
I have a for loop to evaluate theta from 0 to 2*pi (for theta=0:pi/180:2*pi). While the for loop runs, the position of point B is stored in a previously initialized, empty array (B=[]). The resulting array is 4x1 and I would like to extract only the first 3 rows to obtain the x,y,z components of the point's position. I intend to then use these x,y,z components to plot the path of the point using plot3(x,y,z).
Can anyone help me to extract the first 3 rows from the 4x1 array? Also, from this new 3x1 array, what would the arguments be in order to use plot3(x,y,z) properly?
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### Antworten (1)

Sindar am 23 Okt. 2020
To extract the first three rows:
B3 = B(1:3,:);
x = B3(1,:);
y = B3(2,:);
z = B3(3,:);
But, if B is really 4x1, then you only have a single point
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