RFormula
R中公式的基本格式：
response variable ~ explanatory variables
响应变量~解释变量。
~读作"is modeled by" or "is modeled as a function of."
符号列表：
| symbol | example | meaning | |||
|---|---|---|---|---|---|
| + | + x | 包含变量，分隔预测变量 | |||
| - | - x | delete this variable | |||
| : | x : z | include the interaction between these variables | |||
| * | x * z | include these variables and the interactions between them | |||
| / | x / z | nesting: include z nested within x | |||
| \ | \ | x | \ | z conditioning: include x given z | |
| ^ | (u + v + w + z)^3 | include these variables and all interactions up to three way | |||
| poly | poly(x,3) | polynomial regression: orthogonal polynomials | |||
| Error | Error(a/b) | specify an error term | |||
| I | I(x*z) | as is: include a new variable consisting of these variables multiplied;I(x^2) means include this variable squared, etc. In other words .I( ) isolates the mathematic operations inside it. | |||
| 1 | - 1 | intercept: delete the intercept (regress through the origin) |