Replace values within a range to zero

Hi,

I have an array 26X106 that contains both positive and negative values.

I want to be able to replace the numbers within a specified range to zero - e.g., all numbers >0.25 and <0.25 are replaced by zero.

Any help would be greatly appreciated,

Thanks!

[Walter Roberson]

You only want to keep values that are exactly 0.25? exactly equal is the only value that is not less than and not greater than.

[Edward Keavney]

I would like to keep the negative values that are equal or less than -0.025 (i.e., -0.03) and keep the positive values that are equal or greater than 0.025 (e.g., 0.03) - all the values between the range would then be changed to equal zero.

Answer 1

[sudobash]

Hi!

This is how to select numbers from a matrix in a given range.

matr = rand(5)

matr = 5×5

0.5725 0.3692 0.6680 0.1522 0.6984 0.3249 0.3382 0.9941 0.8481 0.4326 0.8804 0.6613 0.0909 0.6754 0.1913 0.6391 0.3758 0.8331 0.7947 0.5164 0.8831 0.9587 0.7263 0.6760 0.8337

mask = matr < 0.25 & matr > -0.25

mask = 5×5 logical array
   0   0   0   1   0
   0   0   0   0   0
   0   0   1   0   1
   0   0   0   0   0
   0   0   0   0   0

Selecting in this manner returns a logical matrix commonly known as a mask matrix. You can then set the values at those locations to 0 like this.

matr(mask) = 0

matr = 5×5

0.5725 0.3692 0.6680 0 0.6984 0.3249 0.3382 0.9941 0.8481 0.4326 0.8804 0.6613 0 0.6754 0 0.6391 0.3758 0.8331 0.7947 0.5164 0.8831 0.9587 0.7263 0.6760 0.8337

Hope this answers your question.

This article talks about some basics of matrix indexing in MATLAB.

[Steven Lord]

You can also do this using the or operator | instead of the and operator &.

x = 1:10;
tooSmall = x < 4

tooSmall = 1×10 logical array
   1   1   1   0   0   0   0   0   0   0

tooBig = x > 7

tooBig = 1×10 logical array
   0   0   0   0   0   0   0   1   1   1

reject = tooSmall | tooBig

reject = 1×10 logical array
   1   1   1   0   0   0   0   1   1   1

keep1 = ~reject % Could also be written

keep1 = 1×10 logical array
   0   0   0   1   1   1   1   0   0   0

keep2 = ~tooSmall & ~tooBig % not too small and not too big

keep2 = 1×10 logical array
   0   0   0   1   1   1   1   0   0   0

x(reject) % 1, 2, and 3 are too small; 8, 9, and 10 are too big

ans = 1×6

1 2 3 8 9 10

x(keep1) % 4, 5, 6, and 7 are just right

ans = 1×4

4 5 6 7