CODEWITHSUNDEEP
rreshapemelt
neversaint
neversaint

Reputation: 64074

How to melt a selected single column in a data frame

With this code:

dat <- structure(list(Probes = structure(1:6, .Label = c("1415670_at",
"1415671_at", "1415672_at", "1415673_at", "1415674_a_at", "1415675_at"
), class = "factor"), Genes = structure(c(2L, 1L, 4L, 5L, 6L,
3L), .Label = c("Atp6v0d1", "Copg1", "Dpm2", "Golga7", "Psph",
"Trappc4"), class = "factor"), FOO = c(1.133, 1.068,
1.01, 0.943, 1.048, 1.053)), .Names = c("Probes", "Genes", "FOO"
), row.names = c(NA, 6L), class = "data.frame")

I created the following data frame:

        Probes    Genes   FOO
1   1415670_at    Copg1 1.133
2   1415671_at Atp6v0d1 1.068
3   1415672_at   Golga7 1.010
4   1415673_at     Psph 0.943
5 1415674_a_at  Trappc4 1.048
6   1415675_at     Dpm2 1.053

What I want to do is to select last column and melt it into like this:

FOO 1.133 
FOO 1.068 
FOO 1.010 
FOO 0.943 
FOO 1.048 
FOO 1.053

How can I do that?

I'm stuck with this code:

library(reshape2)
melt(dat[,ncol(dat)])

Upvotes: 3

Views: 1939

Answers (1)

akrun
akrun

Reputation: 887981

We can use stack after selecting the 'FOO' column.

stack(dat['FOO'])

Or

melt(dat['FOO'])

The dat[,'FOO'] is not a data.frame. It is a vector. We can find the difference between [, [[ etc in the ?Extract. When there is a single column, the default option with [ is drop=TRUE. We can specify drop=FALSE if we are using the , to specify the row index.

stack(dat[, "FOO", drop=FALSE])

If we don't know the column name, just use ncol

stack(dat[ncol(dat)])

The difference is in how we are using it and the object returned.

Upvotes: 4

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