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lets say I have the following dataframe:

Ensembl_ID          A   B   C   D   E   F   G
ENSG00000236601.2   0   0   0   1   0   0   1
ENSG00000237094.12  2   187 442 109 88  144 486
ENSG00000269732.1   0   0   0   0   0   0   0
ENSG00000284733.1   0   0   0   0   0   0   0
ENSG00000233653.3   0   0   0   0   0   0   0
ENSG00000250575.1   1   11  17  5   5   8   17
ENSG00000278757.1   0   0   2   0   1   0   7
ENSG00000230021.9   0   25  30  27  9   8   11
ENSG00000235146.2   0   0   0   0   0   0   0
ENSG00000225972.1   0   7   3016    11  5   14  5
ENSG00000225630.1   1   113 194 76  91  47  94
ENSG00000237973.1   25  1037    9767    1160    886 1321    5220

What I would like to do is only keep the ~top 50 highly variable genes:

I thought it would be like this: dif_genes <- order(apply(df, 1, var), decreasing=TRUE)[1:50] but that leaves me with a vector containing variances without genes.

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1 Answer 1

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One way is adding a new var column to your original data frame and sorting the updated data frame by the newly introduced column:

df$var <- apply(df, 1, var)
df[order(df$var, decreasing=TRUE),]
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  • $\begingroup$ the OP wants top 50. I would suggest df[order(apply(df[, -1], 1, var), decreasing=TRUE),][1:50, ] to avoid adding the variance as a sample (in case OP wants to do a heatmap) and removing the names that seem to be in the first column. The key @user16197 to keep the top 50 genes is the comma after the 50; it tells R that this is a 2D data. $\endgroup$
    – llrs
    Commented Sep 27, 2022 at 22:27

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