TwoSampleMR-R教程 两样本孟德尔随机化（原来真的就是这么简单……）

1. 工具变量

install.packages("remotes")
remotes::install_github("MRCIEU/TwoSampleMR")##To update the package just run the command again
install.packages("readxl")
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读取本地文件

1. 方法1：先改变量名，然后format_data()读取自己整理好的工具变量文件，命名如下图。注意，命名区分大小写，不正确则无法读取
   

##name:SNP	beta	se	effect_allele	eaf	exposure	chr	position	gene	pval	samplesize	mr_keep
HcyIV <- as.data.frame(read_excel("IV_Hcy.xlsx"))
library(TwoSampleMR)
Hcy_exp_dat <- format_data(HcyIV, type="exposure")
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2. 方法2：直接用read_exposure_data()读，然后code改。尽可能提供多的信息，方便后期画图

HcyIV.2 <- read_exposure_data(
  filename = "IV_Hcy2.csv",
  sep = ",",
  snp_col = "SNP",
  beta_col = "beta",
  se_col = "se",
  effect_allele_col = "effect_allele",
  #other_allele_col = "a2",
  eaf_col = "eaf",
  pval_col = "pval",
  #units_col = "Units",
  #gene_col = "Gene",
  samplesize_col = "samplesize"
)
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3. 最后改好自己的暴露名

Hcy_exp_dat$exposure <- "Homocysteine"
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工具变量必须为独立变量。根据参考文献选择ref人群和r2

## Clumping via IEU GWAS database
Hcy_e
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