When performing statistical tests, you can transform your variables by using mathematical expressions.
One common example is to use the logarithm of a variable. Let's say you are studying a biological parameter with a very large spread from 10 to 1.000.000. Instead of using the raw value, you might want to analyze the logarithm of this value to reduce the range to 1 to 6 instead of 10 to 1.000.000.
How to use transformations?
1. Click on the cog wheel next to the name of the variable:
2. Then, head to the transformation menu:
Use a logarithmic transformation
Logarithmic transformations are available from the transformation menu as described above.
Just pick the logarithmic transformation you want. Then validate by clicking on the "Confirm" button.
Beware! If you have 0 or negative values, the logarithmic transformations will not be applied and an error message will be raised.
Other mathematical expressions
A wide range of mathematical expressions is available to transform your variables.
To use a custom mathematical expression:
- Choose "Custom" in the transformation menu
- Type a formula using "x" for the variable, for example: "x + 100" to add 100 to your variable
Operators
Expression | Definition | Comment / Example |
---|---|---|
+ | Plus | x + 100 |
- | Minus | 100 - x |
* | Multiply | |
/ | Divide | If the variable data contains 0, an error will be raised and the formula will not be applied |
** or ^ or pow | Power | x ** 2 is x squared |
% | Modulo | |
== | Is equal to | |
!= | Is not equal to | |
> | Is greater than | |
< | Is lower than | |
>= | Is greater or equal | |
<= | Is lower or equal | |
and | And | To be used with the "if" expression |
if(a, b, c) | If "a" then "b" else "c" | if(x>=100 and x<=200, x, 100) If the value of the variable is between 100 and 200, then we use the variable. Else, we define the value as 100. |
in(a, b, ...) | Belongs to | if(x in (1, 2, 5), 0, 1) If the value of the variable is 1, 2 or 5, then we define the value as 0, else we defined the value as 1 |
not | Not | if(not(x in (1, 2, 5), 0, 1) This expression will have the opposite behaviour of the previous example |
or | Or | if(x==1 or x==2, 0, 1) If x is 1 or 2, then we define the value as 0, else we define the value as 1 |
xor | Exclusive Or | https://en.wikipedia.org/wiki/Exclusive_or |
Functions
Expression | Definition | Comment / Example |
---|---|---|
abs(x) | Absolute value | |
acos(x) | Arc cosinus, x in radians | |
acosd(x) | Arc cosinus, x in degrees | |
asin(x) | Arc sinus, x in radians | |
asind(x) | Arc sinus, x in degrees | |
atan(x) | Arc tangent, x in radians | |
atand(x) | Arc tangent, x in degrees | |
atan2(x) | Two-arguments arc tangent | |
ceil(x) | Upper-value rounding | Rounds to the closest integer greater than x ceil(2.3) = 3 |
cos(x) | Cosinus, x in radians | |
cosd(x) | Cosinus, x in degrees | |
exp(x) | Exponential | |
exp(x, base) | Exponential in a specific base | |
fac(x) | Factorial of x | |
floor(x) | Lower-value rounding | Rounds to the closest integer lower than x floor(2.3) = 2 |
log(x) | Logarithm | |
log(x, base) | Logarithm in a specific base | |
max(x1, x2, ..., xn) | Maximum value between x1, x2, ... | max(x, 100) will always return a value greater or equal to 100 |
min(x1, x2, ..., xn) | Minimum value between x1, x2, ... | min(x, 100) will always return a value lower or equal to 100 |
pyt(x, y) | Pythagorian value of x,y: sqrt(x^2 + y^2) | |
random(x) | Random number in [0, x] | |
round(x) | Integer rounding | Rounds to the closest integer round(2.3) = 2 round(2.7) = 3 |
round(x, n) | Rounding to n digits | |
sin(x) | Sinus, x in radians | |
sind(x) | Sinus, x in degrees | |
sqrt(x) | Squared root of x | |
tan(x) | Tangent, x in radians | |
tand(x) | Tangent, x in degrees |
Constant values
Constant | Definition | Comment |
---|---|---|
E | Euleur's number | ~ 2.71828 |
PI | Pi π | ~ 3.141592 |
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